With Straight Talk, the service works best in the activation zip code area.
They may not have great coverage when you go out of town.
You can check their coverage here: https://www.straighttalk.com/wps/portal/home/h/coverage/servicearea
Have you checked with Straight Talk to see if there are any coverage problems or ongoing maintenance in the area?
All you can try is to back up all of your information and do a factory reset on one of the phones.
If that works successfully, then try it on the other phone as well.
Ok, have you tried the factory reset?