Do they have Quicktime installed, per the program's requirements?
(Although the Quicktime Player is considered risky software, it's possible -- and necessary -- to install Quicktime's other components in order to edit MOV files.)
No the don´t... And I have... Aha: that's probably the problem. Should´ve figured that one out myself :facepalm
But how to install the components without getting the safety issue?
You just install it, watching each prompt screen, and opting out of the Player.
If that doesn't work, just install the whole thing and then change the suffix to the QuickTimePlayer.exe file to something like .bak to disable it. The Player is only dangerous on your system if you actually play videos with it.