You can do this manually. Just specify two different ports. (And better also specify different names on the commandline too.)
So for instance you write
simutrans -server13353 -server_name=Exp1 -load game1.sve&
simutrans -server13354 -server_name=Exp2 -load game2.sve&
That does not need any script. And Timothy's script can only handle a single server, since it only stores exactly one pid. You could run it from two different locations, but I would not use the script then. it should not kill simutrans randomly.
If you server is a virtual server, it may run in main memory limitations. The supervisor software will then kill one processs after a short grace period. Use "top" or "htop" command or something like that to check the memory consumption.