I am not sure I have the topology down. But it looks like you have multiple VPN that you want to be able to communicate directly between them. This will take a few steps.
VPN configuration
For this setup, you will want to create route based VPN. If the other side is also an SSG or an SRX, you can have these with the default proxy-id being open and no other configuration would be needed on the VPN. You simply create the route to each network to the tunnel interface and they will be able to reach each other.
If the VPN is to another 3rd party vendor the VPN itself will need proxy-id pairs setup that match ALL the pairs of networks that need to talk to each other. And need to be configured on both sides.
Security Policy
These will need to be configured to permit the traffic. On the SSG you set each tunnel to a zone and then need a policy that permits the zone to zone traffic for the sites.