Musk turtle don't get too big, the largest I've seen was about 6ish inches long. Turtles are messy though and I wouldn't keep 2 in anything smaller than a 40gal tank (bigger is better). They will need a heat lamp on one end of the tank and place to climb up on and bask in the light. Keep in mind that you will still need to do regular maintenance on the tank, meaning weekly water changes or more depending on how messy they are.