I myself only use BYOD (bring your own device) pay-as-you-go VoIP carriers. No contracts, no fees, no commitments.
I then use the Linksys SPA2102-NA VoIP ATA with built-in NAT-Router and QOS.
I then configure the ATA for service with my preferred BYOD VSP (Voip Service Provider).
These providers usually allow all account users to make calls to each other for free (know as "In Network Calling).
You can setup an account for each of your family members.
Then buy an ATA for each family.
Then configure each ATA with their account login info.
From there on, the devices are plug-n-play.
Send the ATA's to each family member and it should just be plug-n-play when they get it.
For best results, the Linksys SPA2102-NA should be connected directly to the Internet Modem. The Modem should not have a built-in Router. If the Modem has its own built-in router, things get a little more complicated.... Like Port-Forwarding issues.CQVoIPhttp://www.cqvoip.net