Xl2tp+ipsec+iptables - how to set up access on a subnet with the same address space?

Question

iptables

In general, there is xl2tp, which distributes IPs to clients 192.168.2.5-255.
Clients have local IPs in 192.168.1.X, clients behind different routers via dhcp.
The task is to have access to each other between clients (works), and to have access to the subnet of an arbitrary client under other clients. How to check this? Noob in routing, sorry(