And lets not forget that Mom stated that she had always been able to send and receive texts to/from Dylan at Dads prior to this. Dylan's friends would also know whether or not Dylan could send and receive texts from Dads.
Do we have any idea how many times Dylan had stayed at the house in Vallecito prior to the family moving in July?
I see we've now got three visits between MR and Dylan after the move. How often did they see each other before? Why wouldn't CR have wanted to go on the August vacation to Boston and NY?