Ok, I'll bite on this one. I'm going though my own grandparents issues, so forgive if I vent a bit...
Grandparents are NOT parents. They have no RIGHTS bestowed on them LEGALLY because they happened to live long enough to see their offspring reproduce. Grandma, it's great you have money and you were doing all this when the child was living with you. BUT, and a big BUT here, you need to realize that you have been helping DAD (the one with legal rights) in raising his child. Dad still has the rights, and he can take the child wherever and whenever he pleases. Because you have money doesn't mean he has to do what you want. And yep, as a GRANDPARENT, sometimes you have to hold your tongue and bite it til it bleeds. Was he harming the child physically? If not, you got nothing and you will probably have to eat a lot of crow before dad is going to trust you again after kicking out. If you are really THAT concerned about the child, then maybe you should have been not spending as much money on kiddo and helping dad get more education to secure a better job and help them get back on their feet as their own family, which helsp promote their parent-child relationship, and still gives you that grandparent relationship. Your job is to HELP them, and I will guarentee you, if you try to legally go after the child, you can kiss goodbye ever getting to see child (especially if dad has sole custody) again. Until the child is 18. You are NOT the parent anymore and you need to take a step back and realize that. Your job ended when your child hit 18. Dad is TOTALLY being responsible and took HIS child with HIM when HE moved out. He's providing for the child. And food stamps are the governments way of helping. Nothing wrong with that at all. Lots of nuclear families use food stamps.
Take a long hard look at what you have done. Yelling in front of a child, while yes it encourages yelling, does NOT a bad parent make. You even admitted it wasn't directed at the child. Courts would say so what?? So because dad did things you didn't like you kicked him out. Grandma, you might, and probably will, find a lawyer that will tell you how great your case is and they will take it. All they are doing is taking your money. They need to eat too and you are only helping them. MAYBE you should talk to a counselor about this (cause multi-generational families have a slew of issues when living under the same roof) and then contact dad to sit down to a discussion with the counselor and TALK LIKE ADULTS. If you guys could work this out then you can continue to help them and not pay the mortgage payment on a lawyers vacation home.