In order to achieve your requirement, you need to establish PEPVPN between Surf SOHO and Surf on the GO, at the same time, enable Layer 2 PEPVPN bridging.
This will make networks behind Surf SOHO and Surf on the GO in the same broadcast domain.
enable dhcp server in Surf SOHO to server DHCP ip range
establish PEPVPN to Surf on the GO, enable Layer 2 PEPVPN bridging too
Surf on the GO:
the wan ip is 192.168.52.146
the lan network is 192.168.60.0 / 24
the lan interface ip address is 192.168.60.254
disable the dhcp server in Surf on the GO
establish PEPVPN to Surf SOHO, enable Layer 2 PEPVPN bridging too
When you connect a device to Surf on the GO, it will get the DHCP IP address from Surf SOHO.
In this case, the device might get the IP address 192.168.60.10/24 and the gateway of 192.168.60.1 from DHCP server at Surf SOHO.
Due to this, when the device behind Surf on the GO wants to go to internet, the internet traffic will go back to Surf SOHO and then go out to internet.