Need Help with Homegroup Bullshit

Hey all

So I'm trying to set up a private network to share files between my laptop and my desktop via LAN while still using WIFI for internet. The WIFI is through the uni so I can only have one one connection at a time but I can share it through my desktop to my laptop. The problem is when I try to set up file sharing on the desktop it won't only share through LAN and tries to share with everyone else on the WIFI network. Was also wondering if there was a way to make it permanent because it's a pain in the ass having to set it up again any time one is disconnected or shut off. Especially when you aren't allowed to change settings yourself and are forced to the wizards and troubleshooters. 

Any help is appreciated.