Great! But, I'd still be worried that it is too big for them. It would have been better to divide the 10 gallon. Especially if you find them cruising their tanks constantly - big indication of stress.
If you have some $, you can go to Staples and buy 2 4L Really Useful Boxes for $7.99 each then put them on top of the UTH in your tank so that one end of each box has heat. You can use a screwdriver to punch a few holes in the containers.
If you can post a picture of your set-up that would help us give you better advise...