Dear Kamal,
You are wishing a happy marital life for your sister like any concenred brother. But going by your posts it seems that you are spoiling your sister's marriage and your sister is helping you in the mission. Please make your sister understand that the in-laws are her own folks and its her family. Give her the confidence that she can resolve the issues as she is adult, mature, educated and employed. Educate her that she should not come up with petty issues to you. Once she starts believing that the in-laws family belongs to her and performing household work there is actually taking care of her house and family..... then see the change in behaviour of in-laws.... also with that she will get respect from her family.......
Two years are not a long period....... give her time to adjust with her family.... do not try to control her life...
One question: Does marriage was performed with her consent? or was against her wishes?
Do not go for police or court procedures...... it will only strain and ruin relationships.....