Use cotton plugs for ears. This is normal. All do like this. Society will ask for reason why their daughter left husband and came, so then they cant tell the fault is theirs, they will tell husband not proper, his dad not proper, his mom not proper, floor not proper, that this, and bad mouth like this. For this you have to adopt same strategy, you also bad mouth about them. No legal remedy for this. You can file defamation case on them, but thats of no use. Just buy some cotton and put it in your ears. Try giving police complaint against them for bad mouthing you all.
Police will call them and warn them, but they cant be behind them all of the time. Like that you will need separate police station for your familial problems, he told like this he told like that, she told like this, like that this that give complaint as and when possible, and police run behind them holding plaster to shut their mouth !!...
Doing like that will start a almost never ending legal battle and marriage of brother will end then and there, and roaming to court for next 7-8 years will start.
You may open your own police station would be my advice :-))