That woman is stealing my son/brother. “That woman” being the daughter in law. I really don’t understand how she can steal him. She has come wanting a husband wife relationship. She does not want the same relationship as you have with your son/brother. So how can she steal him? That would mean you no longer have any connection with him but she can’t ever take away the fact that he is your son/brother.
But what people do need to understand is that things change when a person gets married. He is no longer single and cannot continue to live as though he is single. He now has responsibilities to look after and maintain his wife. Just like you want your husband to give you priority in his life so should you allow your son/brother to give his wife the time she deserves.
He has a duty to be good to you and he should continue to do so. It is upto you and your son/brother to ensure you maintain your relationship. But to make the wife the enemy will only drive a wedge between you and your son/brother and that will be your doing. In this process you may also destroy his marriage. Instead support your son/brother to be a good husband and see how close he will be to you.
And lastly, remember that for someone to be able to steal something you must first have to own it, and you do not own your son/brother. He belongs only to Allah.