So sorry, OP. My parents split when I was a teenager, but a lot of the same issues are a problem. The best thing I can tell you is that you have a lot of company in this. People whose parents are married just won't understand what you're going through, and may be very judgmental. But there are a lot of us adult children coping with divorce fallout, so welcome to the club.
To answer your questions:
I split visit time half and half. I do visit a bit more because they are divorced, but there's only so much I'm willing to do. If they want more time they are welcome to visit me. It's sad because my own children get a lot less time with their grandparents due to the divorce. But there is little I can do about it.
Kids-- I dunno. Mine are too little to ask. But of course, your kids will have friends with divorced parents, which would likely cause them the same concerns. I think all kids these days have to recognize that parents divorce and their parents might too.
Upkeep-- it really depends on the situation. Are your parents remarried, do they have other family nearby, what is their living situation and health, etc. They will probably need to re-do their medical directive etc., so if you can twist their arms to get that done, you'll be in better shape when a crisis occurs.
The best advice I can give you is to maintain your boundaries. Resist stepping up into a caretaking, spousal-type role if it isn't truly necessary. They need to realize they can't expect as much of your time and attention, because you are having to care for both of them separately. So encourage them, even to the point of letting them struggle a bit, to find their own support system and take care of themselves. Otherwise you will have more than you can handle as they age. When they talk to you about things, listen sympathetically but do not jump in as a problem-solver.