I've had my 2 ornates housed together in a plastic tub since they were quarter-sized. They don't attack each other or anything but that's probably because they're well fed.
Probably. Its extremely risky with these frogs being such veratious eaters. I've seen videos of Pyxies kept together as well. As many as 5 adults. In the same large enclosure. I see that as way more risky than Pacs.