Hello,
we need to install a firebird 2.1 database-service automatically on
our customers windows pc's without affecting the firmness of
(possibly) existing firebird or interbase installations.
We found documentations for installing "multi-instances" of services
using "instsvc.exe". But if we consider the following precedence path,
there is still a lack of clarity:

"For Windows servers and clients the precedence path is:
1. The FIREBIRD environment variable
2. The RootDirectory parameter in the configuration file
3. The registry setting HKLM\ SOFTWARE\Firebird Project\Firebird
Server\Instances\DefaultInstance, field DefaultInstance.
4. The directory one level above the one where the server binary is
located"

Our questions:
- What impact has a FIREBIRD environment variable for firebird 2.1
services, pointing to the wrong installation?
- How can we manipulate the service to search in "The directory one
level above" even if the FIREBIRD environment variable is set?
- If our firebird-service has a custom name, is the registry setting
for "DefaultInstance" still considered?

futhermore
- Is there a possibility to use in "firebird.conf" and "alias.conf"
solely relative pathnames?

Thank you.

PS: we did even consult our newly bought "The Firebird Book"
(including supplement for FB 2.1). But unfortunately unsuccessful.