Ways to relax?

I'm 18 and I'm 22 weeks pregnant. I still live at home bc me and my fiancé can't afford a place. My grandmother has dementia and lives with us. She just had knee replacement and has to have supervision 24/7. So me and my mother switch off on things. I've been so stressed out and barely resting. I haven't gotten to take a nap in forever or sleep well at night. On top of all this my two nieces and nephew are here for spring break and I'm having to do everything for everyone and I'm breaking down constantly. I am trying my best to help and not be negative because my mother needs help and my brothers 17&12 won't do anything. Any advice for me to quit breaking down? I need a way to relax or find a way not to feel so overwhelmed.