You may need to come and talk to us to get it running as there are a few tricks and we may have them all documented (did I mention documentation?):
I'd imagine that your network isn't running correctly if it can't resolve those repos.
The wiki page is a big of a mess (volunteer to update it?). You probably want to look at the bits here:
## This is safer to be done directly on tty, not via ssh:
Get rid of Network Manager and then reconfigure the network. It takes a bit of jiggling about to get that configured and settled after which it is easier - this is usually taken care of on first install from ISO but you are kind of coming in part way through so it needs some effort.
You have a Rocket account so please talk to us there. It's much easier to help 'on the fly' than here.
Things are in a constant state of flux, particularly with the build system so you may need a hand.