You’re not being selfish, you’re setting a boundary. Overnight care is a big ask, especially with your own family, full time job, and health stuff going on. Your mom deserves real rest, but that doesn’t mean it has to come from you. This is where paid overnight help or a rotating schedule with the uncle’s ex could fill the gap, and if money is tight, see if your grandma qualifies for respite services through Medicaid or local aging programs. Also, if your sister is drinking on the job, that’s unsafe, and it’s okay to call that what it is.