MacEnstein. Welcome to discussions!
Best to start a new question - many people will stop looking here since it is marked answered. This lets you get the attention you deserve and keeps one problem per thread.
But - we are here - so let's see what happend.
Bonjour will find computers on the same network. That means unless you have gone to pains to set up two DHCP servers and change things substantially - things will work on most home networks.
Open the terminal application on both computers and do a
netstat -nr - each should have the same gatway for the default destination and same network destination (look for 192.168.1/24 or similar) under the Gateway column where it says link#4
Most likely you will have IP addresses like 192.168.1.1 and 192.168.1/24 - feel free to start a new thread or post your netstat -nr results of it's not clear what I'm doing.
Also - you can simply test this out from the command prompt. Each machine is known by a host name - type
hostname -s on each. If Bonjour is going to work - machine "a" should be able to ping machine "b" as follows:
ping b.local
the .local says use Bonjour to find the machine named b and ping it.