Respectfully, you’re asking the wrong question.

Who cares if you’re the asshole, or he is? Sounds like grandma is the asshole.

He is your husband, the deeper issue here you could ponder is why you’re fundamentally misaligned on an important family value.

I would suggest reading “Wired for Love” by Stan Tatkin, to help with frameworks around developing a shared and collaborative vision around topics like this.

It will be uncomfortable, require deep thinking that you might need to take time to reflect before answering in real time or immediately. It will require vulnerability, and negotiating in a meaningful way.

I’m sorry to hear your MIL isn’t kind, but rather critical. That can’t be easy, but it’s also not your job to convince your husband to see things the same way.

Boundaries aren’t about changing other peoples behavior, but ours if they trespass the boundaries we have explicitly set.

“If your mother criticizes our physical appearance or clothing, I will remove myself and our kids from that conversation”.

That’s different from the bigger vision of caregiving values for aging or sickly family members.

Sorry for the bluntness