Before parenting the Instance to the players, create a clone that will be given, instead. This will ensure that the initial GuiObject remains unmodified while also allowing as many players as you’d like to receive the same GuiObject:
Example:
for _, player in ipairs(playerList) do
local clonedFrame = Frame:Clone()
clonedFrame.Parent = -- Directory of the intended ScreenGui for each player
end
You can’t parent something to 2 parents, as something can only have one parent, you have to clone the frame you want to give to both of them, as @StrongBigeMan9 mentioned