I don’t want to work sundays no more?

So I’m currently working two jobs. A full time job and a part time job. And I’m currently working 7 days a week and I hate it. I work from
7:30-4 Mondays through Fridays at a cemetery then whenever we get a funeral on a Saturday I work that day aswell. Then on Tuesdays and every other Friday I work from 5-8:30 at a restaurant as a cook and on sundays I work from 1:30-5 I don’t mind working Saturdays at my full time job because it’s super easy and I’m making overtime plus I can bring my dog to work on Saturday so I actually really like it. I’ve been working like this for over a year and it was alright but then we got a new cook that took my sundays for me. But last Wednesday he walked out and now im scheduled to work sundays again and I don’t want too because I want a day off. We are now down to two cooks and they want me to step up but I want to step down but I feel bad because the other cook already works at that job 50+ hours a week and now her dad might be dying. I don't know how to break the news. I’d like to say “I can no longer work sundays” but then they will just put it on my other coworker who already works at that job way to much.
I don’t want to work sundays no more?
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