If the address is already in use, this likely means that another copy of MultiChain is already running on the second node, and this should be stopped first.
Another less likely possibility is that MultiChain's random choice of node for P2P connections just happens to clash with some other service running on this system. You can do this to find out:
telnet localhost <port>
Where <port> is the number after the colon in the node address retrieved from noe 1.