Is possible without VPN? / Initial Setup

Hi,
I want setup freepbx, and my question is if is possible without VPN, i am hosting it on a VPS (Vultr.com) and i guess all ports are open…

My finality is create a extension for each person of my family and maybe some good friends.
And i will connect too to Sapo/meo VoIP service (trunk i guess) to external connections (like +351.21xxxxxxx)

I already tried to setup but not successful i can’t connect to other extension. but i did the same with elastix and i can connect/register with my SIP Client in my Computer only, but still can’t call to other extension…

Any help will be apreciated, thank you very much…
and sorry for my english, i’m portuguese