Seven net balanced adsl lines and 2 with static IP

Good evening to all.
Premise by saying that I thank anyone who wants to spend some time to help me.
I have 7 ADSL lines balanced by Zeroshell … the output goes into a Mikrotik Routerboard RB1200 which, together with a Radius server to handle accounting.
So far so good … users who are engaged in wifi with PPPOE navigate according to their profiles.
The problem is born now that there are two lines with a range of public static IP to be assigned to those who request it.
I connected these two lines to the switch (which is also connected to the LAN cable that comes from RouterBOARD which in turn takes the band offset by Zeroshell) that houses the main wifi antenna (the repeater).
After the first leg, the other two antennas bring the band in two different countries and one of these has another Mikrotik RouterBOARD (RB800) that manages its PPPOE customers, not to weigh the mikrotik headquarters.
The result? That all users are connected only to the two external modems … so a lot of users managed by only two adsl, with Zeroshell is bypassed.
How can I solve this problem? I was told that I only have a PtP link that goes to the main repeater, and that can only do one job at a time: either the band or door handles PPPOE customers. But I do not understand what the problem is: why can not I also enter the two adsl with public IP in Zeroshell?? So I would have the balance of 9 instead of 7 adsl and I would have the opportunity to assign public ip to both countries managed … help me! I do not understand anything …
Excuse for my bad english…