When my family experiences a D in it, they take sides. Preferrably the side of the blood relation. It may be nothing more than this. My mom's mom let my dad stay with her until my mom told her it made her uncomfortable. I remember her telling me that she had told him to find an apartment. She said SIL, I love you, but my daughter is my blood. I have to stick with her.
It may be something like that. Perhaps next time stop and talk to them, let them know that you and your H are still amicable and they don't have to choose sides.
