Admin commands are not working properly..?

Eh, here let's start over, your script doesn't seem correct but your on to something.

First let's setup the variables and the event.

local owner = {game.CreatorId}
local admin = {}

game.Players.PlayerAdded:connect(function(plr)

end)

Next let's create a variable inside the event and then check through each id to see if the plr's id is in one of the tables

local owner = {game.CreatorId}
local admin = {}

game.Players.PlayerAdded:connect(function(plr)
    local isin = false
    for _,v in pairs(owner) do
        if v==plr.UserId then
            isin=true
            break
        end
    end
    if isin==false then
        for _,v in pairs(admin) do
            if v==plr.UserId then
                isin=true
                break
            end
        end
    end
    if isin==true then
        print("he's in")
    end
end)

Expanding on Danz script; you can also use a dictionary array, which would allow you to check the table without running a for loop each time.

local admin = { 
    ['azarth'] = {creator = true, id = 312625920};
    ['danzlua'] = {creator = false, id = 12345};
}

-- Note that CreatorId will be 0 in studio.

local function player_joined(plr)
    local index = admin[plr.Name:lower()]
    if index then 
        if index.id == plr.UserId then 
            if index.creator then 
                print( string.format("%s is the creator", plr.Name))
            else
                print( string.format("%s is an admin", plr.Name))
            end
        else
            print( string.format("%s is a(n) %s, but the UserId didn't match.", plr.Name, index.creator and 'creator' or 'admin'))
        end
    end
end

game.Players.PlayerAdded:Connect(function(plr)
    player_joined(plr)
end)

-- Catches the players that joined before PlayerAdded connected.
for i,v in pairs(game.Players:GetPlayers()) do
    player_joined(v)
end