Why am I receiving red circles with an x when I try to text a family member on the same plan

[AC Question]

We use the same phones. It's an Android XT901 Motorola and we've had no problems until today. Texts sent to other people are fine. But each text sent to one phone is not received, yet it is to the other.
Thanks for any help you can provide.

 

[B. Diddy]

Welcome to Android Central! Have you discussed this with your wireless provider?