Now that you have changed your original question I have removed my first answer.
The following extracts have been taken from the website of the UK Law Society, and are very relevent to your case.
I have removed certain parts of Sections 3 and 4 since they were not relevent to your case. Anything that I believe you should pay particular attention to I have written in capitals for emphasis:
Note: Whenever you see the word ‘client’ this will be your father.
2.5 Religious choice
Some clients are domiciled for succession purposes in England and Wales, but still wish to pass their assets in accordance with Sharia rules for religious reasons.
Such clients may prefer a Sharia compliant will, notwithstanding the freedom of disposition provided by English law.
Provided the will is signed in accordance with the requirements set out in the Wills Act 1837, there is nothing to prevent an English domiciled person choosing to dispose of their assets in accordance with Sharia succession rules (subject to any potential claim under the Inheritance (Provision for Family and Dependants) Act 1975, which only applies where the deceased died domiciled in England and Wales).
You will have to obtain probate on the Sharia-compliant will, in the normal way. - See more at: http://www.lawsociety.org.uk/advice/practice-notes/sharia-succession-rules/#sthash.YXxKppoK.dpuf
- Drafting a Sharia compliant will
In order to prepare a Sharia compliant will, you need to understand how the estate is applied under Sharia succession rules.
First, the cost of the burial and any debts are paid.
Secondly, a THIRD OF THE ESTATE MAY BE GIVEN TO CHARITIES OR INDIVIDUALS WHO ARE NOT OBLIGATORY HEIRS.
Finally, the remainder is given to a defined set of 'primary' and then 'residual' heirs.
3.1 Payment of burial expenses and debts
The estate pays the expenses of enshrouding and burial of the deceased, and then must fulfil any monetary or religious debts the deceased may have had.Once the debts have been paid in full, the testator can distribute the balance of his estate.Top of page
3.2 THE ‘FREELY DISPOSABLE THIRD'
Up to one third of the remaining wealth may be allocated on fulfilling the legacies of the deceased.
This is known as the 'freely disposable third', which can be distributed to charity or to INDIVIDUALS WHO ARE NOT HEIRS UNDER THE SHARIA RULES OF SUCCESSION.
Certain rules apply to this 'freely disposable third'.
First, A VALID WILL IS REQUIRED IF THE TESTATOR WISHES TO MAKE GIFTS TO NON-HEIRS: without this, the whole estate will be distributed according to the Sharia rules of succession.
However, the testator is under no obligation to do this, and may if they wish leave their entire estate to the Sharia heirs.
Secondly, the testator cannot make bequests as part of the freely disposable third to people who will already receive a bequest as an obligatory Sharia heir. In other words, they cannot try to favour one heir by using the freely disposable third to give them more than the amount they are entitled to under Sharia rules. However, this principle can be overridden if all the other Sharia heirs give their consent. Finally, ANY BEQUESTS TO NON-HEIRS WILL ONLY BE VALID UP TO A MAXIMUM OF ONE THIRD OF THE ESTATE.
If a gift exceeds one third of the estate's value, perhaps because of changes in asset values, the maximum one third will be given and the rest will fall into the residue to be distributed to the Sharia heirs.
It is possible to give more than one third to non-heirs but ONLY WITH THE CONSENT OF THE SHARIA HEIRS or if one of the default provisions mentioned below applies.
The remainder of the estate (a minimum of two thirds) is divided between the Sharia heirs.
As with many civil law jurisdictions, Sharia rules have a system of pre-determined heirship. Each heir receives a predetermined proportion of the entitlement, depending on the number and nature of the heirs who survive. This means it is not possible to say in advance who will inherit: it is only at the date of death that the division can be calculated.
There are two main types of Sharia heir.
First, a portion of the estate will be distributed amongst the obligatory or primary heirs: those individuals whose share has been prescribed in the Sharia.
Secondly, the remainder will be distributed between the residuary beneficiaries
Primary heirs (Please note: I have removed the females heirs in this section simply because the grandchild in your case is a male)
The male heirs are:
Father; Grandfather; Uterine Brother (half brother on mother's side); Husband
At first glance, the list of primary heirs may seem incomplete, particularly as it does not include sons or full brothers. That is because sons and full brothers are residuary beneficiaries, who receive their entitlement after the primary heirs.
There are different types of residuary beneficiaries, but the most common are those related by birth to the deceased, being male relatives whose link to the deceased is not solely via a female. As well as fathers and sons, this will include full brothers of the deceased.
If there are no residuary heirs, then the entire estate is divided between the primary heirs pro rata to their original entitlements.
If there are no primary heirs and no residuary heirs, the estate goes to more distant relations: blood relatives of the deceased who are neither primary heirs nor residuary heirs. - See more at: http://www.lawsociety.org.uk/advice/practice-notes/sharia-succession-rules/#sthash.YXxKppoK.dpuf
YOU WILL SEE FROM THE ABOVE THAT THE GRANDSON IN QUESTION IS NOT A PRIMARY HEIR, ALTHOUGH HE MAY WELL QUALIFY AS A RESIDUARY HEIR. IT APPEARS HIGHLY UNLIKELY THAT THE BOY COULD LEGALLY INHERIT YOUR FATHER’S HOUSE UNDER SHARIA, SINCE THE PRIMARY HEIRS ARE ALMOST CERTAIN TO ‘SWALLOW’ MOST OF THE ESTATE AS PART OF THEIR DUE INHERITANCE.
- Lifetime gifts and trusts
There are generally no limits on what a Muslim can give away during his or her lifetime; however, you should ascertain WHETHER HE WISHES THE TRUST TO BE SHARIA COMPLIANT.
4.1 Gifts on death bed or in terminal illness
The only restrictions on lifetime giving are when the individual is suffering a terminal illness or is on his or her deathbed. In this case, the individual is treated as having effectively died already, so the Sharia succession rules apply. Any attempt to undermine an heir's entitlement in these circumstances will lead to a claim by the deprived heir in paragraph 3.5.
4.2 Other lifetime gifts
In all other cases, however, the Muslim client can freely make lifetime gifts, of any amount and to any person. There are however certain religious limitations.
A MUSLIM CANNOT MAKE GIFTS THAT CONFLICT WITH THE RULES OF THE SHARIA: for example, a Muslim could not make a donation to a gambling establishment or to set up a pub, as both concern strictly-prohibited activities.
4.3 Lifetime trusts
This freedom of lifetime giving means that there is nothing preventing a Muslim client setting up a lifetime or inter vivos trust, unless the settlor is on his or her deathbed, or has a terminal illness.
However you should ascertain whether the lifetime trust is intended to be sharia compliant.
THERE MAY HOWEVER ALSO BE TIMES WHEN A MUSLIM CLIENT (in this case your father) IS ATTEMPTING TO USE A LIFETIME TRUST TO PASS ASSETS TO NON-HEIRS, OR TO FAVOUR SOME HEIRS OVER OTHERS.
- Further information
5.1 Practice Advice Service
The Law Society provides support for solicitors on a wide range of areas of practice. Practice Advice can be contacted on 020 7320 5675 from 09:00 to 17:00 on weekdays or email firstname.lastname@example.org.
5.2 Sharia scholars
Local Sharia scholars are a useful source of information and may be contactable via the client's mosque.
There are various websites, including islamchannel.tv, inheritance.ilmsummit.org and lubnaa.com, that provide an Islamic inheritance calculator, to determine the percentage entitlements of the surviving heirs. These require details of the heirs who have survived the deceased, in order to calculate the sharia fixed and residuary shares of the estate.
Please note: The Law Society cannot guarantee the accuracy of the entitlement calculator and it should not be substituted for expert legal advice.
At first glance it would appear that what you father is attempting to do is against the Sharia. However, these matters are very complex and so I urge you to seek direct legal advice from a solicitor, ideally, from one who specialises in UK inheritance law and sharia law.
By the way, you have misunderstood my original comment.
What your father has done is perfectly legal under UK law. His grandson cannot take ownership of the house until he is 18; nevertheless it can be bequeathed to him on trust.
If your father decides to ignore Sharia and press ahead under UK inheritance rules then his Will (if deemed valid) will be enforced by the courts.
You could appeal, on the grounds that it was unfair….after all, you are the son; but not on the grounds that the Will is illegal.
Valid wills carry great weight under UK law. Several years ago a woman bequeathed her entire estate (worth over one million pounds) to her cat …..to be held in trust. The family appealed….and lost!
I hope this helps.