Making a server farm to render using 2 older Mac mini and 2011 MBP

I own OSX server. The two minis are a late 2009 with 8 GB RAM and the horrible 2014 with 4 GB (yes, thought I could upgrade :-( ) and a MBP with 16 GB and an SSD. I am thinking of upgrading the minis to SSD to speed things up. 2009 now only plays music in the bedroom, the 2014 was just a file server and we use it to watch NetFlix on our big TV. Both beachball for the simplest things.

I do not mind putting SSDs in both. The OWC SSDs are around 30€.

I do not understand how server farms actually work. I have an Ethernet hub which is unused.

Can anyone point me to an article that explains how it is done? JFYI, I am 70, but been using Macs for 31 years. However, I am the posterboy for Mac and the RTFM. I still keep a copy of 10.6.8 on my 2011 to run Garageband 5.1 (What a simple interface, so easy to use.)

We have two more MBP but these are 2017 15" and 13" both touchbars top of the line loaded. Can these be added to the farm and have the farm running in the background using any excess CPU and Ram to the load?

As always, Thanks in Advance.