Turtle/tortoise help?!?

I have a box turtle and a Russian tortoise together in a 50 gallon tank. We live in the Mojave desert so it gets up to 110 degrees in the summer and below freezing in the winter so I don't think having them outside is safe. Everyone says they need so much space but all I can possibly fit in my house is the 50 gallon tank. So how can I make it as comfortable as possible. Also, what is best to feed them an such. They always eat the turtle pellets I get at Petsmart and they get lots of veggies and lettuce and cabbage but my box turtle only eats the pellets. She won't even eat the worms I give her. And she gets a bath every week so what else can I do for them. Any care tips and ideas are helpful.