My in laws don't understand we need our space: Advice?

My in-laws are asking us to come over for dinner every weekend. It gets to be so much. My husband and I already work opposite schedules since he has retail hours and I have a standard 9-5 job. We already have a shortage of time together since he has to do some nights and weekends. My MIL wants us to let our son have a sleepover at least once a month. She has no visitation rights, and it’s not like I’m in a position where I want time away from my child. I enjoy spending time with the 3 of us, and that is what is getting me through my dad’s health issues and this pandemic. We can’t see my family because my dad has critical health issues and can’t get covid or any other illness since it would be detrimental. They don’t seem to understand that we need space, and they are always calling and inviting us over. It gets stressful because you don’t want to disappoint them, but it’s so much. Help.