My mother and my husband do not get along, and I am the permanent bridge

My mother has lived with us since my father passed in 2021. My husband agreed without hesitation and I will always be grateful for that. But they have never warmed to each other. She thinks he is careless with money. He thinks she interferes with how we raise our son. Neither says it to the other. Both say it to me. Every single day I carry messages, soften things, explain one to the other. I am exhausted. I cannot ask her to leave, she has nowhere to go and I would never. I cannot ask him to change what he feels. Has anyone found a way to step out of the middle without the whole house collapsing?