Would it be wrong of me to try to convince my SO to cut his mom off?

My SO and I have a one year old and I am pregnant. His relationship with his mom is strained because she lives on the opposite side of the country, doesn’t really talk to him, and was a shitty parent when him and siblings were younger. But he says it’s hard to cut her off because he hopes she changes one day, so I feel bad saying anything.

She has two teenagers that she does not have ANY custody of and a few years ago, got a charge for kidnapping because she tried to take them out of state without the dad’s permission. When I was pregnant with my son, she begged my boyfriend to bring them out of state for her, claiming they were being abused. We talked to one of the kids and they said that MIL was lying and trying to manipulate the younger child into lying about being abused. I told my SO that if he got involved, not only would I be gone, I would report him myself.

Now, MIL is begging my SO of the same thing, again claiming they are being abused. And, again, when we talk to the older sibling, she says that she has no idea where MIL is coming up with what she’s saying. I told my SO to stay out of it and let her take her allegations to a lawyer, because if they are serious and she wants the kids that bad, she will. Or would try to get the kids herself. But she hasn’t, which raises red flags to me. She hasn’t even visited them in over 3 years.

I am kind of annoyed because my gut feeling is she thinks if she can get someone else to do it, they’ll be the ones who face any punishment. And I’m annoyed that she’s okay with it being her son who is about to have two kids and already has one very young child. I feel like she must not really care about him at all if she is risking him like this and I want her out of our lives. (The reason we don’t trust her versions is because she actually neglected my SO and his siblings, let them go without food, they always had lice, etc.)