Brother, it is important that you take time to talk with all parties involved.
Talk to your wife by setting aside a special time when you can tell her about your observations and how you feel. Allow your wife to speak of her feelings first and encourage her to voice her perceived ideas about the family members she has trouble accepting. Ask her what it is exactly that makes her feel the way that she does. Listen to her. Do not become frustrated or annoyed. Just listen quietly. Disengage emotionally if you can. Let your wife do most of the talking. Do not interrupt. Confirm your understanding of what she is saying by repeating her feelings back to her. This will ensure that you are listening closely and that you have understood her views.
Once your wife has finished communicating her feelings to you then tell her how this all makes you feel. Do not accuse or blame. Tell her that you are looking at ways of resolving this issue and that everyone concerned will need to make an effort.
Next, find time to speak to your mother alone. Ask her the same questions and listen closely to what she is saying. Do the same as for your wife.
Finally, do the same with your brother and his wife.
Once you have heard everyone out, you can begin the task of mending bridges and regaining peace in the family. Everyone will have to be willing to participate. The one who objects will most likely show themselves to be the problem so observe the behaviours.
I have seen this similar problem in families come up again and again.
The mother does not like the wife or the wife does not like the mother. Whichever way it goes, the outcome is the same: discord in the family.
Women ought to be more careful with families.
I want to say a few words about respect which you are looking for from your wife towards your family.
Respect is 2-way. Your wife should respect your family BUT they should respect her same. There is no difference or favouritism here. If you want others to respect you, you've got to respect others first.
So, does your wife respect your family?
Are there reasons as to why she has lost respect? Was it there to begin with? If everyone is kind and accepting of her then your wife needs to work on her issues. It really then means that the problem lies within her and you can all do what you can to support her.
Always keep in mind the goal: to have a happy marriage and to provide a safe and caring environment for your children. They are the Muslims of tomorrow, you love them and want them to be happy.
The next question is 'Does your family respect your wife?'
Was your family welcoming and accepting of your wife from the beginning and do they hold her with much regard?
They should be kind towards her and they should hold her in high regard. It isn’t always easy for a young wife to come and fit into a new family. The family should make a special effort to help here.
Your wife is your wife and the mother of your children and that accounts for a lot.
A note to mothers (I wish every mother could read this):
We know we have to hold you in high regard and love you because you are our mothers. We love you for Allah's sake.
Allah SWT says:
And We have enjoined upon man, to his parents, good treatment. His mother carried him with hardship and gave birth to him with hardship, and his gestation and weaning [period] is thirty months. [He grows] until, when he reaches maturity and reaches [the age of] forty years, he says, “My Lord, enable me to be grateful for Your favour which You have bestowed upon me and upon my parents and to work righteousness of which You will approve and make righteous for me my offspring. Indeed, I have repented to You, and indeed, I am of the Muslims. 46:15
And our beloved prophet rasool saws sallalahu alay wasallam reminded us as in the following Hadith:
A man came to the Prophet and said, ‘O Messenger of God! Who among the people is the most worthy of my good companionship? The Prophet (PBUH) said: Your mother. The man said, ‘Then who?’ The Prophet said: Then your mother. The man further asked, ‘Then who?’ The Prophet said: Then your mother. The man asked again, ‘Then who?’ The Prophet said: Then your father.
Islam gives special priority to good treatment and respect of our parents, especially mothers.
But here is a problem:
Some mothers are under the GREAT misconception that because they ARE mothers, they can behave as they please within the family.
This is wrong.
Being a mother does not give you a special licence to throw your weight around, creating power struggles with the son’s wife.
Creating unhappiness and discord and breaking up a family will not be pardoned for a mother, the same as it won’t be for anyone else. (It will be according to Allah SWT’s will and do not forget that He IS JUST). Mothers should be careful and not transgress limits set out by Allah SWT. If a marriage breaks up because of a mother’s relentless interference, and disapprovals, then this deed rests on her shoulders and she is held accountable.
To hold a marriage together is a priority for the sake of pleasing Allah SWT and for the sake of the children.
In addition to the above advice remember that there is no more powerful tool than duaa. Use it and ask of Allah SWT. He will hear any duaa that has a good intention in it.
I wish you all the best in resolving this issue because I know how serious the consequences can be.
May Allah SWT guide you and the whole family in resolving your problem. Salaam brother.