Help needed finding info on load balance based on IP subnet

I am looking for any documentation on how I can load balance based on IP subnet
It’s difficult for me because the subnets that I want to load balance are on another router

Example:
All customers with IP in subnet 10.10.0.0/24 uses ISP1 on ether2
And all customers with IP in subnets 10.1.3.0/24 & 10.12.0.0/24 uses ISP3 on ether3

Here’s my network setup:

ISP1 At&t router “12.xx.xx.65” to MikroTik ether2
ISP2 Quest DSL router “192.168.0.1” to MikroTik ether3

MikroTik Router
Ether1= local 192.168.200.1
Ether2=ISP1 12.xx.xx.66
Ether3= ISP2 192.168.0.100

MikroTik Ether1 to TinyWiFi router ether1

TinyWiFi Router
Ether1=192.168.200.6
Wlan1= 10.1.3.0/24 given static to customers PC or Router
10.1.5.0/24 given static to customer CPE’s
10.1.6.0/24 given static to Towers
Wlan2=Not used


Two towers that have MikroTik Routers

Harguth
Ether1= local 192.168.0.1 Not used
Ether2=Not used
Ether3= Not used
Wlan1= 10.1.6.17 connection to TinyWiFi
Wlan2= 10.10.0.0/24 given static to customers PC or Router
10.11.0.0/24 given static to customer CPE’s

Singlestad
Ether1= local 192.168.0.1 Not used
Ether2=Not used
Ether3= Not used
Wlan1= 10.1.6.18 connection to TinyWiFi
Wlan2= 10.12.0.0/24 given static to customers PC or Router
10.13.0.0/24 given static to customer CPE’s