iPad sending to iPhone via iMessage
It's hard to figure out what's the actual problem without more information or being at the scene. Some simple fixes you may try:


Restart your iPad.
Make sure you are not in airplane mode.
Make sure you have interact connection. You can test by browsing a webpage.
Go to 'Contact's and double check if their phone numbers (including country code) and/or apple id emails are correct.
Test whether you can message others. If so, it might be your family's side's issue.