The current setup is this: the gateway acts as an arp proxy from the 188.8.131.52/16 subnet that ul uses to the 184.108.40.206/24 subnet that skynet uses.
This has the following problem: if we add a second gateway, it'll also be in the 220.127.116.11/24 subnet, and therefore the first gateway will still try to do proxy arp for it, causing general badness.
If we want to have a redundant gateway, we have two choices:
have the backup gateway not be addressible
re-subnet our subnet to work around this
(A) is undesirable as we lose the ability to access the backup gateway externally, which will be needed if the primary gateway falls over and the failover fails. Therefore, (B) is the way forward.
Move the gateways to the 18.104.22.168/28 subnet (host IPs 22.214.171.124 -> 126.96.36.199) for their external interfaces. Specifically, the active gateway should be 188.8.131.52, the backup gateway 184.108.40.206, with the static IPs for the gateways being 220.127.116.11 and 18.104.22.168. The subnet mask will be 255.255.255.240.
All other machines will be moved to the 22.214.171.124/26 subnet (host ips 126.96.36.199 -> 188.8.131.52). This has the advantage that they won't need to change their IPs, just their subnet masks and gateways (i.e. we don't have to change dns for a start).
The gateways internal interfaces will also be moved to the 184.108.40.206/26 subnet. The active gateway should be 220.127.116.11, the backup gateway will be 18.104.22.168, with the static IPs for the gateways being 22.214.171.124 and 126.96.36.199.
How/Why it works
There is no longer any problem with having multiple gateways. They are only trying to do proxy arp for the internal IPs, which are in a different subnet to the gateway IPs.