Hovering over player does not work?

So this likes to appear the billboardgui over the baseplate and it won't go away. I don't get this. What am I doing wrong? The point is, hovering over a player should show their FirstName and Surname according to a DataStore that is always set if they're in-game and past the introduction where you pick your name. It literally just doesn't work at all properly and it's unexplainable. In starterplayerscripts:

local plr = game.Players.LocalPlayer
local Mouse = plr:GetMouse()
while wait(0.5) do
	if Mouse.Target ~= nil then
		if Mouse.Target.Parent:FindFirstChild("Humanoid") then
		plr.PlayerGui.BillboardGui.Enabled = true
			plr.PlayerGui.BillboardGui.Adornee = Mouse.Target.Head
			plr.PlayerGui.BillboardGui.FirstName.Text = game.ReplicatedStorage.getfirstname:InvokeServer(game.Players:GetPlayerFromCharacter(Mouse.Target.Parent))
			plr.PlayerGui.BillboardGui.Surname.Text = game.ReplicatedStorage.getsurname:InvokeServer(game.Players:GetPlayerFromCharacter(Mouse.Target.Parent))
		else
			plr.PlayerGui.BillboardGui.Enabled = false
			plr.PlayerGui.BillboardGui.Adornee = nil
			plr.PlayerGui.BillboardGui.FirstName.Text = "FirstName"
			plr.PlayerGui.BillboardGui.Surname.Text = "Surname"
		end
	end
end

in serverscriptservice:

function game.ReplicatedStorage.getfirstname.OnServerInvoke(plr)
	return game:GetService("DataStoreService"):GetDataStore("FirstName_1"):GetAsync("user_"..plr.userId)
end
function game.ReplicatedStorage.getsurname.OnServerInvoke(plr)
	return game:GetService("DataStoreService"):GetDataStore("Surname_1"):GetAsync("user_"..plr.userId)
end

Please help!

Unfortunately, I don't have 5 score yet, so i can't comment, but I think you have a few problems here: The functions cannot be triggered. To make a function trigger while declaring it you go:

game.ReplicatedStorage.getfirstname.OnServerInvoke:connect(function(plr)
-- code
end)

Also, getfirstname/surname sounds like a function, so it would most likely be :GetFirstName() or :GetSurname(). Also, Mouse may need to be activated before you can do something, but I haven't had any experience with mouse hover yet, so don't trust my suggestion. There may also be a few syntax probs in there, but it's too cluttered for me to find them.