A wife who does not respect your mum wont respect you at all. You are a product which has come out of that factory called as mother, without her you were not been able to exist. Your sole existence depends only on your maker ie the mother. If your wife does not respect your mother, kick her out, neck her out, throw her out.
IN your case, file for divorce directly based on mental cruelty. Bargaining for best price for your freedom you can do later as the case progresses. Keep one time lumpsum settlement as the last option for mutual consent divorce which will get over in 6 months time. All the best.