Don't try to make peace. You might not know the half of what's gone on and might make things worse again. If they have reacted like this to some unsolicited advice, how might they react to some well meaning but unwanted peace-making tactics?
You have asked us if we think they are cutting them out, and it sounds like they are distancing themselves to me. But it doesn't sound like you've spoken to them and heard their side of what went on. And unless they volunteer that information, don't assume you know or plunge in and ask them.
To the outside world, I could be your sister in law. If you listen to my MIL, I have never liked her, never made her feel welcome and cut her out overnight by making up a lot of lies about her.
If you listen to me, I had ten years of unwanted advice, bullying and harassment from her that culminated in outright cruelty, with MIL asking me, three days after a stillbirth "if it still hurts to give birth if your baby is dead." She never mentions that when she's telling the world how awful I am to cut her out, or the fact that I still tried to make a relationship work with her for a further two years after that comment (and it wasn't the only comment of that type) until the day that both MIL and FIL took turns to rant and and bully me over the course of several hours and I collapsed with a panic attack. They've tried to end my marriage, they have lied and twisted and controlled and manipulated.
And although I've said that here, most of the family have no idea what really went on, only have MIL's side of things, and believe I'm absolutely evil to have cut her out "overnight" and "for nothing."
What you know about might only be the tip of the iceberg and peace-making wouldn't sit well with me. If I hear the phrase "yes but they are still family" or "they are to old to change..." I will scream. MIL was only 48 when I married DH, she's 60 now, and I don't think that counts as too old to change or as "getting on a bit" and it's not just that I won't see them now, I can't, not without feeling sick at the thought and on the verge of another panic attack. They really are that bad.
Don't get involved, it only ever makes things worse.