That process (faxsend) must be from a 3rd-party fax product. It may have configuration tasks to add the new ports. Check that out first.
The only other suggestion I'd have would be to run "ditty -a" on one of the existing modem ports, then configure the new ports in the same fashion.
# ditty -a /dev/ttya12
{lots of output}
# ditty /dev/ttya02 -fastcook -ixon (etc. etc. etc)
You can add the "printer" value to your ditty command. This normally forces the port to remember it's values through various processes. Check for entries in the start-up scripts (/etc/rc2.d/*, /etc/rc.d/8/*, /etc/inittab) for any commands dealing with the existing ports.