Assalaam Alaikum wa rahmatullah,
Dear brother, my thoughts go out to you if what you are stating is the truth, then by the truth of Allah Subhana wa ta’ala, these people are wrong in their dealing with you and this matter.
Foremostly, do not fear the cursing as no unrighteous matter will ever be accepted by Allah Subhana wa ta’ala as He is the MOST JUST, THE BEST JUDGE and His Compassion is with the TRUTHFUL.
Dear brother, your first error was not having witnesses to witness your transaction and not having it in writing.
To avoid failure of memory and to reduce the chances of misunderstanding and bad faith, the Qur'an commands the writing of financial deals and/or having the deal confirmed by witnesses. The Qur'anic commandment is contained in the following two verses, the first of which is the longest verse in the Qur'an:
"O You who have attained to faith! Whenever you give or take credit for a stated term, set it down in writing. And let a scribe write it down equitably between you; and no scribe shall refuse to write as God has taught him: thus shall he write. And let him who contracts the debt dictate; and let him be conscious of God, his Sustainer, and not weaken anything of his undertaking. And if he who contracts the debt is weak of mind or body, or is not able to dictate himself, then let him who watches over his interests dictate equitably. And call upon two of your men to act as witnesses; and if two men are not available, then a man and two women from among such as are acceptable to you as witnesses, so that if one of them should make a mistake, the other could remind her. And the witnesses must not refuse (to give evidence) whenever they are called upon.
And be not loath to write down every contractual provision, be it small or great, together with the time at which it falls due; this is more equitable in the sight of God, more reliable as evidence, and more likely to prevent you from having doubts (later). If, however (the transaction) concerns ready merchandise which you transfer directly unto one another, you will incur no sin if you do not write it down.
And have witnesses whenever you trade with one another, but neither scribe or witness must suffer harm, for if you do (them harm), behold, it will be sinful conduct on your part. And remain conscious of God, since it is God who teaches you (herewith) - and God has full knowledge of everything." (2:282)
"And if you are on a journey and cannot find a scribe, pledges (may be taken) in hand: but if you trust one another, then let him who is trusted fulfill his trust, and let him be conscious of God, his Sustainer. And do not conceal what you have witnessed, for, verily, he who conceals it is sinful at heart; and God has full knowledge of all that you do." (2:283)
Dear brother, you should speak with your wife and sit her down and tell her the truth and ask her to support you. Is your divorce final? If you can in any way salvage your marriage for the sake of Allah Subhana wa ta’ala and your children. Do not allow the dishonesty and deceit of others ruin your family’s happiness and rob your children of a united family.
As you have already stated your truth and it WAS heard (although rejected), you have done what you could. Leave the matter in Allah Subhana wa ta’ala’s hands for He is the best judge. Do not make your own life miserable any longer, place your trust in Allah Subhana wa ta’alah and seek His guidance. Be patient.
The truth always conquers over lies and dishonesty. You may find that in time, your brother comes to you with regret. It is not easy for those who fabricate lies to live and sleep with them. Turn to Allah Subhana wa ta’ala in the form of duas and you will see how things unfold. Be kind to your parents, they will come to realise their wrong ways and feel regretful about them.
May Allah Subhana wa ta’ala assist you in regaining peace and contentment and good family relations. Ameen.