Pretty sure 12 year old is legal to babysit in most states... 2 days might be a bit of a stretch in terms of time unless you have a relative of neighbor close by/checking in on them, but I don’t know if I’d make a federal case out of it.
I don’t know if I’d personally do it, but a 12 yo and a 9 yo should be able to survive okay for a couple of days.
My parents went somewhere for several days when my brother and I were that age. We went to school during the days, and a neighbor’s teenager, 16 or so, came over in the evenings to help us fix supper, and spent the night. Kids that age can be reasonably responsible, but for that length of time, I think sensible parents would have arranged someone to check on them and be available in an emergency.