I have 5 ISP ip public addresses , 5 Draytek 2860n routers, i want to connect 4 of the router to 5th router i want each router to have it own public ip and each have it own private ip range ,effectively having 5 different networks each having internet connection. i think it can be done just dont know where to begin, many thanks

Set up the IP routed subnet on the main router: https://www.draytek.co.uk/support/guides/kb-drayos-iprouting

Then the other routers would be set up with Static IP addresses on WAN2 from router 1's IP Routed subnet.