From your SSG if you have two external interfaces(say eth0 and eth1) connecting Cisco Router-1 and Cisco Router-2 then it is pretty straightforward. Create 2 Route-based VPN.
If you have only one external interface on your SSG and you are trying to form the VPN between two peers then you need point-to-multipoint VPN. Please check the following document - https://kb.juniper.net/kb/documents/public/VPN/routebasedhubandspokevpn_rev_1_3.pdf