I think they will be fine for 2-3 days max as long as they have water, food, and clean litter box to start with. Just be sure to love them up a lot after leaving them alone for a couple days.
my two cats are funny if I've been gone for a while (I get a cat sitter if I'm gone for two or more days) - they act like they miss me but also like they are mad that I left in the first place