My daughter acquired two crabs a few weeks ago... Man has THIS been a time of learning (and expense)!

We've created a nice Crabitat, read tons about humidity levels, temps, and food. But I'm still not satisfied with their home. I know the temp must be off, because they've dug a little nest right in beside the heating pad and refuse to move! Fall has finally decided to arrive here in Alabama, so our AC isn't running as much and the ambient house temp has been between 72-75°F.
Can someone please help me determine what KIND of crabs we have so that we can improve their tank?
Current tank conditions: 10 gal, eco earth substrate that ranges from 2" to 6" deep, 78-80% humidity (towel over mesh top until I can afford better), temp 75°F using a "mini" UTH attached to the back right side of the tank (nearest the fresh water). I'm having a hard time bringing up the temp in the tank. Suggestions welcome.
Thanks!