So the P2 will effectively end up being (in my example) 10.200.10.0/24 to 10.100.10.0/24.
Each side 'hides' it;s local 10.10.10.0/24 subnet behind another, same sized, subnet. You could use any unused subnet for that I just chose 10.100.10.0 and 10.200.10.0.
So on each side that would be the Binat address.
However if you do not need access between the two subnets dircetly but only from the pfSense_1 OpenVPN subnet this becomes easier. You only need to BiNAT on the pfSense_2 side like:
Screenshot from 2022-05-12 14-02-05.png
On the pfSense_1 side the P2 would be just be 184.108.40.206/24 to 10.100.10.0/24
To access the remote side VPN clients would need to use the equivalent NAT address.