What are you using to read your temps and humidity levels? I use digitals only.

No Bci or Bcc should ever regurg at 90 deg for a hot side.

The one that regurgs-- have you ever had a fecal done? My boas spend about 1/4 of their time on the hot side and the rest on the cool side, but the hot side is still there, and should be. I'd bring a fecal in for that one too.

The new one-- Take a pillow case and submerge in luke warm water. Squeeze out any excess water and then put the boa in it and tie it up. Place him/her over the hot side for about an hour. Let him/her out and repeat this twice a day for at least 3 days. This Will get rid of the stuck sheds and will eliminate any dehydration issues. I mist my enclosures twice to three times a day. Keep the humidity levels at about 60% or so.
One last thing to remember is to feed this new guy/gal smaller meals at first so as not to stress out his/her digestive system. I would not feed him/her till after he/she poops each time you feed him/her till he/she is more acclimated to his/her new surroundings.