Everyone needs respect, if your sister in law and mother in law would like to keep distancing with you, why don't you respect their choice? Why you insist to ask them accept your apologies?
Sometimes, when people say sorry doesn't mean real sorry, they just want others listen to them, for their own good, as "these people" always think they are superior than others.
When you don't want to meet someone, will you say "I don't want to meet you"?. Most of us will say sorry, I'm quite busy, I'm not available, let's catch up later. So all of us are liar?