You guys are clairvoyant and have far better networking acumen than me (as I have proven many times) because the diagram is not so clear for me.

The way it reads for me is that the ISP traffic comes in on the HAPACS with each having their own LANS, which then feed into ports on the edgerouter (which does not seem to have any ISP provider connections WAN comes from hapacs).
Since the chap mentions all as routers I am assuming that the Edgerouter gets ISP1 traffic through hapac2 on network of hapac and ISP2 traffic through hapac3 on the network of hapac3.........
These are WAN inputs to the edge which has is its own lan. The edge router load balances the two WAN connection (one each from hap acs) for its own network.
So the questions I have are.
a. do the hapacs actually need their own LAN network (is anything actually attached to them (devices/users)??
b. my favourite question, why not use vlans
c. is this not simply a question of how to route the traffic from the ISP through the hapacs to the "wan" inputs on the edgerouter.
d. if c is true then we can dispense with NAT on the hapacs (assuming no need for lans on hapacs?
Just a few thoughts to demonstrate I IS CONFOOSED.
I'd rather manage rats than software. Follow my advice at your own risk! (Sob & mkx forced me to write that!)