Hi...hopefully Tigergenesis will chime in soon...she has a lot of experience with sand boas and can probably tell you the best temps to keep them at. I know that for many snakes, temps that are too high can cause them to regurge. Temps that are too low can also cause that. Are you handling them at all before they regurge? If you are, then you may not be giving them long enough to digest their food.

Lastly....once a snake regurges, it takes quite awhile for their systems to recover. It could be that they are repeating the problem because they're not ready to eat again yet. I would wait at least two weeks before feeding such a snake again.

Good luck with them...I hope you get this nipped in the bud and they recover and thrive for you!!!