Idk, are we not adults here?
"She can't make it an issue unless they let it be an issue" is some victim blamey bs, my guy. Yes she can't take the kids by force, but that doesn't mean crossing boundaries from BOTH MIL and FIL doesn't damage their relationship.
You seem very intent on singling out OP as "not wanting a healthy relationship" but also seemingly unwilling or unable to see how there isn't a whole lot of options for a healthy relationship in the first place. Relationship with who?
1) A violent-when-ill MIL who refuses to take her medication, and
2) A FIL who is actively enabling her behavior (thinks she should have sleepovers w/ the kids, disregards their boundaries, etc.).
What's the path forward here? Are they just absolutely lovely people outside this fact? OP was captain of USS Give Her Another Shot and her goodwill has run dry. I get that OP doesn't have the perfect fucking posture or language here, but shit, man.
OP isn't giving up on a healthy relationship. MIL gave up on a healthy relationship when she chose to drop her meds. FIL gave up on a healthy relationship when he decided to enable her.
OP tried to have a good relationship with them, and then they fucked it. She's now asking if she would be the asshole to do what her husband already wants to do, and the answer is no. She's not.