If I am reading this right, you have a remote site that needs to reach AD DS services at a main site. You need to have some kind of connection up between the two sites, do you have a VPN connection? It's not just going to connect the two sites because they have internet. Assuming you have a VPN connection, you need to enable DHCP relay if the computers at the remote site will be getting IPs from the main site's DHCP. If using PFSENSE DHCP at the remote site, you would not need to enable the relay, just make sure that it gives out the proper DNS servers in the scope options. I believe you do need to configure DYNAMIC DNS in the DHCP options in PFSENSE for client registration in DNS, but I haven't used it (I just use MS dhcp/DNS) so I will leave that for someone else here to chime in on.