You could probably use the following settings to get what you want:
ADVANCED, QOS ENGINE, 10 -- QOS ENGINE RULES
I'd try 2 rules, Adults and Kids, or something like that (you might only need one rule to bump Adults up or Kids down). Protocol ANY for both. "Local IP Range" set to the appropriate PCs. Different "Priority" for Adults and Kids.
If you're using dynamic IP addresses for your PCs (the default), then you'll need to force either the Adults and/or Kids IP addresses to always be the same based on their MAC Address using the following:
SETUP, NETWORK SETTINGS, ADD DHCP RESERVATION
Another way of making sure your PC always uses the same IP is to assign a static IP address from within Windows.
Haven't messed with either router setting, but that's what I'd try....