The problem inherent with using Scale positioning is that, although it keeps the guis in the correct percentage of the screen, it doesn't care about the position of any other gui -- often causing them to overlap.
Since you said in the chat that all three guis are inside a single Frame, we can use that to our advantage.
Position the Frame using Scale. This will put it in the correct position on everyone's screens.
Now position the other guis using Offset. The Offset will be relative to the Frame, since the guis are inside it, but because Offset uses pixels instead of percentages, it will keep them all the same number of pixels away from each other.
At least I think this should help.