I want to share
theMasterPlan.txt with Bob and Alice in Google drive.
The problem is that Alice and Bob hate each other. If Bob comes first, he can edit the share list, and block out Alice (or vice-versa). How do I prevent this?
The simplest solution I can think of is to set both of their Share settings to "View" or "Comment". This will prevent either from editing the document.
But my guess is that you are looking for something more like the restricting of "adding" or "removing" by a valid editor. This is also changeable in the "Share Setting" but affects all those the document is shared with.
Open the document's "Share Settings" (located in upper right of document).
Click the "Change" link at the bottom of the "Share Setting" panel.
Select the "Only the owner" option and save.
This will allow all to continue to edit the document, but only the owner of the document will be able to change any permissions.