Custom Chat issues?

I'm creating a custom chat and I'm having lots of issues, for starters the chat messages is not showing up for all the players. I just don't really know how I should do this which is why I was wondering if someone more experience with lua than me could improve on what I have already made

The Current code, found in a localscript in startergui:

repeat wait() until game.Players.LocalPlayer
wait(1)
local StarterGui = game:GetService('StarterGui')
StarterGui:SetCoreGuiEnabled(Enum.CoreGuiType.Chat, false)
---------------------------------------------------------------------------
--Variables
---------------------------------------------------------------------------
local Player = game.Players.LocalPlayer
local Mouse = Player:GetMouse()
_G.moving = false
---------------------------------------------------------------------------
--Functions
---------------------------------------------------------------------------
function createChatLine()
    local textlabel = Instance.new("TextLabel")
    textlabel.BackgroundTransparency = 1
    textlabel.TextXAlignment = "Left"
    textlabel.Size = UDim2.new(1,0,.1,0)
    textlabel.Position = UDim2.new(0,0,0.76,0)
    textlabel.Name = "chatbar"
    return textlabel
end
---------------------------------------------------------------------------
--Global Functions
---------------------------------------------------------------------------

function _G.addMessage(player, chat)
    if (_G.moving == true) then
        repeat wait() until _G.moving == false
    end
    _G.moving = true
    print(_G.moving)
    for _, chatbars in pairs (script.Parent:GetChildren()) do
        if (chatbars.ClassName == "TextLabel") then
            chatbars:TweenPosition(UDim2.new(0,0,chatbars.Position.Y.Scale-.1,0), "Out", "Quad", .5, true)
            wait()      
        end
    end
    local chatbar = createChatLine()
    chatbar.Parent = script.Parent
    chatbar.Text = player.Name .. ": " .. chat
    script.Parent.ChatBar.Text = "Click Here to Chat"
    _G.moving = false
end

---------------------------------------------------------------------------
--Events
---------------------------------------------------------------------------
Mouse.KeyDown:connect(function(Key)
    if (Key == string.char(13)) then
        _G.addMessage(Player, script.Parent.ChatBar.Text)
    end
end)