Help With Player Detection?

What it looks like to me is that your running the function once, immediately when the first player joins. Assuming your doing this, that's your problem. The script runs before/while the second player connects. What you'll need to do is call the function when a new player joins, perhaps like this?

game.Players.OnPlayerAdded:connect(function(player)
    local NumPlayers = #game.Players:GetPlayers();
    if NumPlayers > 1 then
    --- script here
    else
    print("Not enough players")
    end
end)

Of course, that just a suggestion, you should do it however you see fit.

Also, notice how I define the number of players in the 'OnPlayerAdded' function, and not outside of it. This way, the game can check the number of players each time a new one joins. Of course, it wont run/check how many there are if a player leaves, but you can fix that if need be. Hope this helps! :)

local NumPlayers = #game.Players:GetPlayers();
if NumPlayers > 1 then
--- script here
else
print("Not enough players")
end

That's some mean problem that I ran into several times already too. This only checks ONCE if there are enough players. It is supposed to check until the needed amount is reached. So just do it like that:

local NumPlayers = #game.Players:GetPlayers();
repeat
    if NumPlayers > 1 then
        -- script here
    else
        print("Not enough players")
    end
    wait()
until NumPlayers > 1

repeat wait() until is a kind of loop that is supposed to happen until something has happened. Now if it's about the variable itself, you may also try a few other methods. Like table.getn() or even a for loop. table.getn() gets the length of a table, so you could do it like that:

local NumPlayers = table.getn(game.Players:GetPlayers())
repeat
    if NumPlayers > 1 then
        -- script here
    else
        print("Not enough players")
    end
    wait()
until NumPlayers > 1

Hope this helps!