DHCP via GRE tunnel

Hi,
I’m trying to make a GRE tunnel between two office, and it works, the problem i got that i must have the same subnet in both sides, which means same one DHCP server and same network in the both sides.
It works with EiOP tunnel but I wold se if it should works too with GRE.
Any idea?
VISIO_2016-11-15_22-28-49.png

You can only use the tunnel EoIP (layer2)
OR PPTP-L2TP with BCP