You can simply have a table of admins and check when a player joins if they are a part of the table.
local Admins = {3255235235, 124312042, 2144124214} -- UserIds
local currentAdmins = 0
Players.PlayerAdded:Connect(function(player)
if table.find(Admins, player.UserId) then
currentAdmins += 1
end
end)
Player.PlayerRemoving:Connect(function(player)
if table.find(Admins, player.UserId) then
currentAdmins -= 1
end
end