That sounds like it should be controlled by a modifier key. Like click and drag just moves the current window while ctrl+drag moves the parent window as well and shift+drag moves all windows owned by that same program. Right click to cancel the whole move operation from the start of the click, then allow dynamically switching modes mid-drag.
iirc (gnome) tweaks has a toggle for separating dialogs from parents.
That sounds like it should be controlled by a modifier key. Like click and drag just moves the current window while ctrl+drag moves the parent window as well and shift+drag moves all windows owned by that same program. Right click to cancel the whole move operation from the start of the click, then allow dynamically switching modes mid-drag.