I am worried about my dad? Help please?

Your dad is on overload. Poor guy. He needs to remove your sister from his house and not invite her to move in with the rest of the family, even on a temporary basis. If the old house can be rented to a paying renter that will help reduce your dad's financial burden. Your dad needs to take charge of the financial affairs and also of his family. He has the ability to set the rules and control the out comes if he will take the first step. For all your life I hope you will remember this: no one can take advantage of you without your permission.