How can i get a family-license for OS Mountain Lion or install it in a simple manner on my Power-Mac and our MacProBooks without downloading it each time from the App-Store?
Your license is good for any Apple computer you own or control. You can use the original download to create a install USB thumbdrive as well.
If you purchase via the App Store then you can install it on all the computers you own. See How to install Lion or Mountain Lion on multiple computers.
No need for that. You can install ML on all computers you own or control.
Just save the installer to a pocket drive or other media before you do the install. It will be in /Applications.
If you really have a "Power-Mac", you are not going to be able to install ML there.
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