Unable to invite certain family members to events in Calendar on my iPhone

I tried to add an event to my calendar. Family members that I have invited are not getting the invitations.Also, I tried to invite family members, but was unable to add certain members. some cases I search for a family member, their name will come up, but I am unable to click it even though it’s highlighted. Looks like a glitch. also sometimes the app wont allow me to add certain family members even though they have an iPhone or some Apple device.. these family member have been previously invited.

Also, I switched from Verizon to AT&T. I don’t think that has anything to do with it, but not sure if that did something to any setting that I may not know about.

[Re-Titled by Moderator]