My wife's family has 9 siblings and they all have excuses why they can't help take care of their mom and dad. Any advice?

I had to stop my business, to take over the care of her mom and dad because she wasn't strong enough to put her mom in bed, so I took over the 14 hour day shift and her sister is taking the 10 hour night shift. The other kid's live within walking distance, and I live 6 miles away but the other kid's all have excuses why they can't help. But they all got plenty of advice on how to take care of them. The problem is I'm paying $80 a month for gas, and more money for other things . The parent's are just collecting social security and are just getting buy. And all are dead set against a nursing home. I put $ 20 buck's worth of gas in the truck and told them when it's gone the truck is going to set, I can't afford the gas to drive up there anymore, and they will either have to chip in for gas or come and take care of them there self's . So far no money has come and I have about 3 days worth left. I think they think I'm just bluffing but I have no choice but to stop. It's eating me up but all I can do is to tell them the night before that I won't be back till they bring gas or bring gas money. The night shift daughter might have to take off work to stay with them which isn't fair to her. But I got no choice. I am not getting anything to take care of them, and I bring my own food. I'm out of money.