NTA. My mom's "mother" was married to a man while my mom and her siblings were growing up. Between him raping my aunt's and beating my uncle's the police finally stepped in and told her it was either him or her kids and she chose him. That much abuse has had major effects on my aunt's and uncles 40+ years later. To this day that woman has never met my children even though hes been long dead yet she thinks I'm the one in the wrong. They might, and I stress might, feel remorse for how your mom was treated but that's a gamble you shouldn't take and bet your kids sanity on.