SRX5308 with 3 Site VPN-tunnels and internal routing

Hello, all !

I have the setup as following:
Site 1 SRX5308
Site 2 SRX5308
Site 3 FVS336G

These routers have their own local networks with different devices (PC’s, printers, etc.)
Certainly these networks have unique IP-address ranges.

From Site 2 I have two VPN-tunnels - one to Site 1, one to Site 3.

As result, I have access from Site 2 to any network devices at Site1 and at Site 3 (by using IP-address of device).
But the devices (computers) that are located at Site 3 can’t get access to devices at Site 1.
And the devices (computers) that are located at Site 1 can’t get access to devices at Site 3.

I understand that is normal situation for standard Site to Site VPN.
But could you please provide a tips - what additional settings I should apply on my equipment to have access from Site 1 to Site 3 and vice versa ?

Note: I no need direct VPN-tunnel between Site 1 and Site 3.
All internal traffic should follow through Site 2.

Thanks for your attention.