How do you prevent duplicate scripts by only using one script for the whole thing?

You could loop over all the doors.

local doorList = {
	game.Workspace.Dor,
	game.Workspace.Dore,
}

for i, door in pairs(doorList) do
	--Do a door thing
end

If you don't want to manually put all the doors in the table, you could put them all in autimatically at the start of the game.

local doorList = {}


for i, inst in pairs(game.Workspace:GetDescendants()) do
	if isADoor(inst) then
		--add it to the door list
	end
end