QoS will never work, once you hit the internet, that is not a QoS enabled network. Perhaps you need to consider if you have a fast enough broadband speed for your needs.
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As Keith says, this will not really work. Your router is in sync at 79mb, so I'd check what the kids are doing to slow down the connection, any large downloads or file sharing apps etc.
Is your PC using wifi or a cabled connection ?