How to set up Internet distribution through an "external" local network?

Question

Computer networks

OpenWRT on TPLINK. There is an external local area network (for the whole building). There is DHCP: IP type 10.6 .. Everyone connects to the Internet via PPPoE, including me (interface on the router).
Tasks:
1) Distribute the Internet from the router to the "external" LAN to another device (computer).
2) Make external LAN devices visible "from the router".
HAM0 - DHCP client (external locale).
LAN - Ethernet interface for managing the route.
WAN - PPPoE connection.
Inside the external local area, we ping each other. Comp - router, router - computer. Packets are not lost.
How to solve problems? Preferably in the simplest possible way. Details are welcome.