You are getting warmer!
You can check the %iberdir%\Data folder in the way that you suggested, and you can also check it by exploring to that folder, creating a text file, saving it, editing it, saving it and deleting it. You'll want to do that from the server to each terminal, and from each terminal to the server and from each terminal to each other.
This method will show what is having trouble where and perhaps even why. For example, you may get asked to login to the terminals from the server when you path to them to get to the data folder. If you are asked to login, do so with the admin login and you can check the box that says to save the password so that it "sticks."
If you aren't sure what OS the terminals are, that tells me that you have a mixed bag. That will make life more fun (i.e. difficult) for you.
Regarding services, right-click on each one and go to properties and click the log-on tab. You want the settings there to be set to login with an administrator user.
You can get away with using the manager login if it is an admin as you say, but a better practice is to make a user that is for aloha only. This helps a great deal when there is manager turnover and passwords need to change. Even if you don't operate that way now, it's best to be ready in case you do in the future. In fact, I think it makes you more PCI compliant, which is important.
Have your terminals and services use the aloha user all around and things should go more smoothly.