Hello!
I'd like to help you with VPN configuration. I suggest you to use OpenVPN - it's strong, flexible and good VPN protocol.
There are 2 ways how to achieve your goal:
1 - to use separate OpenVPN server, for example on VPS, and connect pfSenses to this VPS. You also will connect to it. This configuration is more stable, in case of down one of sites.
2 - connect first pfSense to second pfSense, and connect users to second pfSense also, and configure routing from VPN users to first pfSense. But in case of second pfSense down you will lose connection to both sites.