I am currently running a node and my son wants to run one at home as well, but they both are set to umbrel.local. What do I do to be able to run both nodes at the same time on the same network?
You have to set a fixed IP for each machine.
See How to set a static IP for your Umbrel machine
Option configuring dhcpcd.conf is easy.
Then to run the Umbrel dashboard just type IP (like 192.168.x.x)