Is it possible to achieve 2 goals using MT routers:

1) Combine 2 LANs (company branches) over secure network
2) Port forward from LAN1 router to LAN2.internalserver.port? ( I want to temporary migrate service from LAN1 to LAN2 without changing it's external IP due to many reasons )

I'm really missing network knowledge to understand what is possible to achieve and how to do it.

What I've did is set up IPSec tunnel ESP connection between LANs, this works fine. I could ping from LAN1 to LAN2 and vise versa. I could ping from LAN1.router to LAN2.router. I could not ping from LAN1.router to LAN2.internal PCs (why?)

Is it possible to somehow setup port forwarding on LAN1 router to LAN2 internal server?

At this moment I've setup LAN1.router -> forward -> LAN2.router external ip and then forwarding from LAN2 external interface to internal network, but is it possible to forward directly to LAN2 from LAN1 router?

I've did this in another way - set up L2TP Server/Client with static IPs, added routes and what is most important - srcnat to l2tp interface to make port forwarding work.