I'm glad to hear that you are doing better.
This is what I think. I think your SIL is a troublemaker. Why is she running to you with these tales and gossip? We often think that people who come to us with "the truth" are our friends, that they have our backs, when the exact opposite is true. She's stirring up drama and telling you things that hurt you. Did she defend you? Did she tell them she doesn't want to hear their BS? Had she not said these things, where would your relationship be with these ILs? How does your MIL treat you face to face? That's what is important.
Are they still ILs? No, but they are your children's grandparents. If they want to be grandparents and they are good grandparents (are they? If they aren't then disregard the rest and protect them), they shouldn't be prevented from being that because that would be good for the children. Besides you, they are the next closest ties to your husband. They can answer questions and keep your DH's earliest memories alive for your children. They can be an ally.
Now, that doesn't mean you have to tolerate abuse. Consider talking to MIL. Let her know you're talking to her because you want a good relationship. "MIL, word got back to me that you thought I didn't appreciate your taking me out to dinner. I just want you to know that I do appreciate the little things you do." "MIL, I'm sorry that you thought I didn't help you enough. I had no idea that you needed more help. Please, feel free to say something to me in the future." And, the most popular, "This week doesn't work for me, but next Sunday would be a great day to visit with the kids."
You can manage this relationship.
Never argue with an idiot. They pull you down to their level and then beat you with experience.