It shouldn't be a problem.

If they are all reading the file at the same time it will be cached, so access will be fast.

You are only reading, so there won't be any locking or trespassing issues.

If you were to update (write) the file there may be an issue, but in your situation there should not be.

The only overhead will be traffic, as potentially the entire file will need to be transferred.

If you want to reduce the network traffic, split the INI file and base the file name on the first letter of the users login.

If you want to be more tricky a modulo hash of the login may give a better spread.