Yes. The connections allowed into a pfSense node from the other end of an OpenVPN connection are on Firewall > Rules, OpenVPN tab.
So on the pfSense server, you would simply not pass connections from 10.0.2.0/24 or 10.0.3.0/24. On Clients 1 & 2 you would pass connections from 10.0.1.0/24.
You can also assign interfaces to OpenVPN servers so you can have a firewall rule tab for each server, instead of all OpenVPN servers combined. This gives you a little more granularity and lets you do things like NAT out a VPN tunnel, etc.
It doesn't have to be three different servers either. You could do it with one Remote Access (At least I think that's what you're describing as Server A) and one Site-to-Site (to go to Clients 1 & 2).