Sinn Fein are right out of the picture and would never attend Westminster so they're not part of the equation. Also, it would be electoral suicide for the Labour party to involve them and they would never let that happen, and I doubt Corbyn et al would be interested anyway. There's nothing to indicate they would.

The DUP are truly the far right lunatic fringe, horrible people. They are bigots, climate change deniers, creationists, homophobes and gawd only knows what else. They aren't fit to be in government but if May's standards are so low as to go into coalition with them, then that's that. It'll still be a rough ride, but with the backing of the DUP then she might make a go of it.