I made a custom sitting animation seat but I have a problem. Help?

The problem here is that once a seat is touched the Humanoid.Seated connection in it persists, it has not been disconnected and will fire for other seats as well. You can fix this by disconnecting the event right after its first run:

script.Parent.Touched:Connect(function(hit)
    if hit.Parent:FindFirstChild("Humanoid") then
    local connection 
    connection = hit.Parent.Humanoid.Seated:Connect(function()
        local animationtoplay = hit.Parent.Humanoid:LoadAnimation(script.Animation)
        animationtoplay:Play()
        local Player = game.Players:GetPlayerFromCharacter(hit.Parent)
        while wait() do
            if Player.Character.Humanoid.SeatPart == nil then
                animationtoplay:Stop()
        print("made by yealetfng please dont steal")
                connection:Disconnect()
            end
            end
        end)
    end
end)

Another way to tackle this is to simply adjust the animation according to the seat sat on from within the connection, in a manner that you don’t have to place individual scripts, all you have to do is place the animation directly under the respective seats:

game.Players.PlayerAdded:Connect(function(player)
    player.CharacterAdded:Connect(function(character)
        local humanoid = character:WaitForChild("Humanoid", 3)
        humanoid.Seated:Connect(function(sat, seat)
            if sat then
                 local animation = humanoid:LoadAnimation(seat.Animation)
                 animation:Play()
            end
        end)
    end)
end)