Hello, everyone! This is my first post.

I have read the advice the members here give, and I am in need of some myself!
My husband cut off all contact with his parents a little over a year ago. They are truly terrible people; this was not a decision made in haste or over one incident. Without going into too much detail, they were extremely abusive to him as a child, and continued to be verbally/emotionally abusive to him as an adult. They do not respect him (or me, but that's not really the issue here!), and lie and manipulate whenever it works to their advantage. After our wedding, at which they behaved terribly, my husband cut off contact with them. They know why he did this, and have not attempted to apologize for anything. I do not believe that they understand that they are in the wrong. Please let me know if more background information would help.
Although it has been difficult, things for my husband as an individual and for ourselves as a family (no kids, other than our dog!) have been MUCH better without his parents in our lives. We have two main issues, which I will try to keep brief (brevity is not my strong suit!):
1. His father's extended family live in the area, and we have had a little bit of a struggle regarding family gatherings. His grandma/aunts/uncles/etc. seem to understand the situation, and appear to support our decision for the most part (other than a few teary "Please call your dad"s in the beginning, it is no longer brought up). They have been very accommodating, and have generally arranged things such that whenever there is a gathering (e.g. holiday, out of town relative visiting, etc.), they hold two gatherings, and invite us to one and his parents to the other. I'm not sure how feasible this is as a long-term plan, and it does mean that we don't see them on the actual holiday (for example, his parents will attend Spring Holiday dinner on the holiday, and we will attend dinner the night before or the night after). His parents are not invited to the event we attend; we are invited to the main event, but everyone knows and understands that we will not attend because his parents are there. We are not willing to attend events with his parents, as it would be impossible to avoid them.
2. My husband's younger sister (a minor teenager) still lives with their parents. They are not model parents to her, but they do not abuse her as they did my husband. She doesn't really know the extent of how poorly they treated him, because she is over ten years younger than him, and he has not really felt that it would be appropriate to tell her, as they do treat her fairly well. She has taken to sending him text messages, saying things like "Mom wants you to call her." We aren't sure if their mom actually says that, or if his sister is trying to play peacemaker on her own. Regardless, my husband generally just tells her that he will call his parents when he is ready. Then his sister will say something along the lines of, "I'm not telling her that. Tell her yourself."

We are looking for a way for my husband to say, nicely but firmly, that she needs to stop doing this. My husband and I have a good rel
ationship with her, and we would like it to stay that way. I think she slightly blames me for the rift, as the cut was made after our wedding, but that's mostly just a vibe I get from her - she has never actually said anything of the sort. I am sort of the opinion that it might be good for him to sit down with her (in person, not via text) and explain what lead to the cutting off of the parents (maybe not in great detail, but enough to say "It wasn't just the wedding."). He is uncomfortable with that, mostly because it is really hard for him to talk about his childhood and we're not sure how she'll react (e.g. she could say she doesn't believe him, which I don't know if he could handle).
I would love any advice/opinions/success stories you may have.