A couple of options for you...
Option 1 (free but requires an iphone and "family" plan):- Register all your family's phones under the same i-Cloud account.
- Hit Settings, then Messages and then Send and Receive. Here you should see your family's phone numbers listed and checked.
- To receive text copies from those phones, check your phone number under Start New Conversation.
Option 2 (monthly fees likely apply):
Use a "child phone" monitoring service, third-party software such as
this one is targeted for this situation; or, you can get something less robust through your particular carrier,
like this one for Verizon or
this AT&T one.
Good luck!