Homemade LAN from scratch

To train, I'm trying to connect three PCs as follows:

• Router: this one is connected to the internet with a USB-ethernet adapter. The built-in Ethernet port is connected to a hub
• Pc1: this is a distro-hopping Pc with 8 distros, connected to the hub
• Pc2: my daily driver, connected to the hub

The idea is to have the router receive all the packets from the Internet through USB and send it to the two other PCs with the hub, on the regular Ethernet port.

Any advice before I start?