I would say the verbal abuse is amongst the hardest.
Is it directed at you? What does the family do when she yells? Maybe we can give some suggestions that have worked in our situations.
There's a helpful book called Verbal Abuse by Patricia Evans that might be useful. One piece of advice that worked for me is to hold up a hand and stay, "Stop" or "No" when someone is on a rampage.
Just like that. And repeat those words (it can feel a bit odd, but it's sort of like communicating with the emotional brain of a toddler).
Another option is to get up calmly and walk into another room. Your point is that you will not be yelled at.
You might be in experimental phase for a bit, trying to figure out what skills will work with all the different dynamics, including how full your cup is.
My sense with your dynamic is that MIL and H are under-functioning because they think you're over-functioning when it comes to SIL. Does that seem accurate?
If you are the one pointing out bad behaviors and processing the emotional toll of SIL, they get to assume a safer position that requires no effort. To keep that dynamic in play, they put up defenses when you mention SIL even though they benefit in a shadowy way from your efforts.
This is a dynamic typical of drama triangles and most of us walk into this trap until we understand how it works. Basically, because you are processing SIL's behaviors for the group, MIL and H don't have to.
That means backing all the way out of the triangle, something that can take many many small steps over a period of time.
An example could be something as simple as: H makes a disparaging comment to you about SIL. Feeling relief that he's experiencing what you experience, you pick up the topic and run with it, agreeing that she is a mess. Except then he expresses annoyance that you're still talking about it, a flip of what he felt when he brought it up. His goal (not conscious) was to unload his feelings, which he did, and now he's irritated that the feeling is coming back at him. That's just an example of how these dynamics can work, it might be different in your exact circumstance.
Your new behavior would be to shrug or express some interest but not say much. The goal is for H and MIL to handle their own feelings about SIL instead of having you carry that load, if that's happening.
It won't help to discuss this with them. It's better to change your own behaviors and see what happens.
The times she has tried to isolate me are hurtful when accepted by others (if that makes sense). For example, when my MIL will call me to say SIL is cooking a thanksgiving dinner for her brother and his children - and seeing nothing wrong with this statement.
Well that's insensitive

Although hosting a dinner that doesn't include you and your family means you can experience Thanksgiving in peace

I may consider blocking off the evening as this is a time a cherish with my kids and want to end the night on a positive note. I have to prepare myself for the resistance I know will come with this. I expect my MIL to push me to have us spend time as one big happy family and blame me if I resist. My H although supportive will agree with her demands to avoid a greater conflict.
If you're still building strength, start small. "Tonight, I need to duck out to do x and y. I'll join you tomorrow night."
Then participate the next night and the next but not the next after.
Small, tiny little changes

I really have to think about what I do for self care.
Honestly, for me, when SD25 lived with us, self care was not warm and fuzzy. It was stuff like locking the door to my bedroom. Because she was in the habit of walking into my bedroom. And bathroom.
Or, it was arranging calls with friends when it looked like SD25 was going to be home alone with me.
H used to sheepishly unload SD25 on me, so self-care was sometimes pre-empting those moves by booking appointments.
When you have someone in your home who has bad boundaries and enablers who aren't protecting you, self care is going to mean protecting your sanity.
You have to carve out pockets of self-care and ensure that they are not negotiable. Eventually, you build enough capital and change enough of the power dynamic it gets easier to do other stuff with less hedging. For me, I had to start small because I was trying to make sure none of my choices created a rift between me and H, which was part of SD's agenda.
I do feel quite alone in my family so it is a bit daunting to have to tackle some of these issues.
That's why this is BPD family

So that you aren't alone in yours.
I have felt so alone and questioned myself so much for so long over all of this
It makes me feel less alone knowing people like you are working through this, too. I'm no longer living with SD but she's in my life and I will always have to manage these feelings and try to land this plane! It's often easier to see a way forward with others but I guarantee I'll be back here asking for advice trying to sort through my own SD shenanigans
