> Can you confirm that it is not possible to run 2 FB servers as 2
> different services?

Let's say it's too difficult to be practicable. You would have to
install the first service, then tweak the Registry to change the
name of the service(s) and then install the second service. I haven't
done it and I don't know if it's working reliably. You would also have
problems with uninstalling the first service (tweak Registry again).

AFAIR the situation will get better with the next Firebird release.
There you can specify the Service name at installation time.

Best Regards

Stefan