1.u cannot prevent anyone from registering a FIR or case against anyone.U can protect anyone after the FIR is registered.after the FIR is registered u can move court seeking for anticipatory bail(AB) for ur family members,there is a minimum chance of husband of getting AB.he must have to surrender to police station or court and apply for regular bail.
2.there is no right of her in self acuired property of father-in-law however claims can be entertained in ancestral property,however the ancestral property get divided between u and ur brother and then she can get share in ur brother's property.
4.the bill regarding this is still not in affect.
5.yes its legal.But claims can be made as in many cases courts have nullified the will deeds,
6.yes she can claim as it become her ancestral property.now if the divorce happened then she has nothing to get.
also consult lawyer for better answers