Text messages sent out by Procare are not received or delivered by some cell network providers. We are currently aware of two cell network providers, T-Mobile and Metro PCS, that do not deliver text messages that originate from email. There are other cell providers that may also use one of those two networks. They would experience the same issue.
T-Mobile offers its customers the option of turning the default bulk text message blocking off. Your parents may follow T-Moblie’s directions on this link: https://www.t-mobile.com/support/plans-features/message-blocking.