Bottom line, do not put them together, and no they are not herbivorous. They can and will eat any fish in with them that is small enough. (That meaning anything that couldn't eat the turtle) Hibernating: no, they would die outdoors where you live without heating. Tank setup: very, very large for each individual turtle (150g) with very good filtration, sand or bare bottom, a dry place completely out of the water to bask with uva/uva light and heat, as well as a cooler dry area. You could also try putting elodea in for something to munch on.