Not all of us are healthy. Not all of us are young. Some of us can't grow a half acre garden each year, raise livestock, cut and split firewood. But we want to survive too!
First of all: I say downsize. You don't need a two story house with 4 bedrooms if the kids are full grown. Maintaining it so they all have a place to come for Thanksgiving and Christmas sounds good but you can't do the maintenance anymore, I doubt the kids are going to do it (they have their own homes to maintain) so that leaves you. You are expected to keep the "family home" even when it has outgrown it's original purpose, you can't make it up and down the stairs any longer, you can't keep it clean, and you don't want to pay the utility bills on a large house when it is just you and the Mrs. and the cat.
It is not up to you to provide a bed and breakfast for your visiting children. If they have to sleep on the floor for two nights, no one is going to die. If they don't help you in the kitchen or offer to go to the store give them directions to the nearest café! DOWNSIZE! Quit waiting on your kids! YOU ARE RETIRED!
Get a one story, one bedroom place you can afford to heat and cool. Take the money you save and take a trip someplace you always wanted to go but couldn't get away (because of the kids). Even if you don't feel like traveling you will have more money to live on. Perhaps, you want to help a grandchild with their dreams. Perhaps there is a cause you always wanted to support. I give to the local animal shelter.
Talk to your children if you can get them to sit still long enough and explain the situation. If they listen that's great. IF they don't do it anyway! YOU OWE IT TO YOURSELF!