Are you wanting to do separate sessions out different com ports or multiple sessions (within a single Dejawin window) to a single host?
If you are talking about using multiple com ports, you can create a shortcut on the desktop to Dejawin then change the command line of the shortcut to put in a different port, i.e. -p=com2.
If you mean multiple sessions to a single machine using something like mscreen on SCO, your choices of terminal types are limited by the mscreencap on SCO. The most common is wyse60. It's easy to add ansi support to mscreencap. I believe the maximum number of sessions in dejawin is 8. It doesn't need to be set anywhere. By default, I believe mscreen allows 4 sessions. You would have to modify mscreencap to get more than 4 but that is pretty easy.