Multi Wan IP and Load Balance/Failover is possible?

[magicool]

Hello,
I need your help to setup my router.
I did this with two routers pretty easy, but now I have a new, more powerful router and I would like to use only one router.
My router is Asus RT-AC68U, Powered by Asuswrt-Merlin 378.55

This is what I have to work with:
ISP1:
IP for connecting to ISP1:
IP: 85.X.X.145 /26
NETMASK: 255.255.255.192
GATEWAY: 85.X.X.129

MY IP RANGE from ISP1:
81.X.X.72-83.X.X.79 /29

ISP2:
PPPOE (username and password, dynamic IP)

This is what I need:
Load balance or failover between ISP1 and ISP2 for IP
81.X.X.74- which will be used for LAN and WIFI (on the same LAN)

and direct internet connection for the rest of IP's:
81.X.X.75-WEBSERVER1
81.X.X.76-WEBSERVER2
81.X.X.77-WEBSERVER3

I do not know where to start with this configuration. I guess it can't be done from the GUI
Please let me know if more details are needed.
Thank you!