wow. No advice as our kids are still under 5. I had friends who took in her half sister (15 yrs old) a couple of years ago, but that was before they had their own children. They'd often find her drunk at the local skate park with her new friends. She ended up moving back interstate after 6 months, but it aged my friends with all of the stress.

Not sure why your dad isn't paying for her upkeep and clothes?
If it's not working for you and your family, I'd be telling your dad that he needs to take back responsibility for her, even if that means having to change his work situation to make it work.