When I saw your post first time, I observed that, some contradictions are there in your statements. Now I understood the cause of your action.
The story is this:
Your parents / mother promised to give a flat on your marriage.
After marriage, they were not in a position to keep the promise.
Though you and your husband ignore the said promise but your mother in law could not. She feels herself a victim of false promise. She orally / phonetically attacks your mother. This causes your mother to attack on you, as it was her expectation that she will get your help in this matter, but you disagreed on it.
Your present status is this:
You and your husband living separately, apart from your mother and mother in law. The party financially self dependent. Spouses are united. Outside attack of mom and mom in law is there.
Solution:
You treat it in number of ways. But the best is, you both have to leave leniency at this juncture.
The husband should tell his mother that, as the flat in question is concerned - “the said flat is our property and we got it. How? Need not to answer.” Therefore now onwards you (your mom in law) never call/talk to her (your mom) on this issue.
Similarly, the wife should tell to her mother that, now onwards, I shall ring you regularly, but please do not ring me, or visit my home, without prior information to me. If there is any call from my in laws please do not attend it. Where the said flat is concerned, - your son in law has enough income to have it one. Just forget about it.
So far court’s interference is concerned, it should be kept out so far it is possible. I hope your straight and clear instruction can stop this fighting between your mother and mother in law. They are fighting in the name of keeping the interest of both of you. You both are unhappy with this.
Action of your mother in law is not so unjustified. She has a feeling of deprivation. But the way she chose clearly attracts the provisions of dowry act.
Action of your mother is also justified. She is anxious for you. Several cases are there where murder and suicide took place. Therefore you ring her regularly at per your as well as her convenience.