I would like to know what ports I need to open up in each firewall so that 2 MVP210s can communicate with each other.

That depends on what protocol you are using.

H.323 protocol uses:

UDP: 5000-5075, 16000-20000 and TCP: 1720, 16000-20000.

SIP protocol uses UDP: 5000-5300.

SPP protocol uses UDP port 10000 or the port number you configure in the phone book configuration and outbound phone book entries.