We have a somewhat older guide that covers the SheepShaver side of things:
https://www.emaculation.com/doku.php/ap ... ntain_lionShort overview of the procedure for later MacOS:
-install tuntaposx
-create a network bridge with your ethernet connection as member.
-set sheepshaver to use the tap networking device instead of slirp
-start sheepshaver, start run ipconfig and add the tap device to the bridge
I haven't done this for quite some time now, so I don't know whether anything above sierra will still allow it.
For your router configuration, refer to its manual.
Best,
Cat_7