From what you provided, you should be able to route the 10.x.x.x traffic down a single VPN connection. Of course it will depend on your VPN device. If your firewalls also support VPN then all you have to do is setup the vpn connection and put the specific subnets on your local side and remote side. Example
Local network 10.100.1.0/24, 10.125.25.0/26
Remote network 10.255.20.128/25, 10.100.2.0/24, 10.100.3.0/24
Then on the other side it would have the opposite networks as above.
Local network 10.255.20.128/25, 10.100.2.0/24, 10.100.3.0/24
Remote network 10.100.1.0/24, 10.125.25.0/26
You just need to make sure you put in the time to look at what IPs are used on each side to setup the correct local and remote subnets for your VPN connections.
Hope that helps