I'm not advertising them anywhere else and they are from the private range. 64512-65534 are the private AS numbers.
EDIT: Each of them advertise a default gateway, withdrawn if their ISP link goes. One of them advertises a routed /29. Two of them advertise a couple of other subnets.
The router that'll take the YouFibre link, the main one, will be routing out to the Internet only. Flows to the networks connected to the other routers will see the first packet from the home LAN go to the primary and it'll respond with an ICMP redirect pointing them to the appropriate router.