over WiFi which works most of the time
This is why people don't run networks over Wifi.
At the start of lockdown I bought a Raspberry Pi which inspired me to install Ubuntu on a redundant laptop to learn Linux. Is there a simple way to include these in the network?
Well, first of all did you get the laptop onto your Wifi? In my experience Linux can be difficult to get working with older laptop hardware.
If you did then https://help.ubuntu.com/community/Samba/SambaClientGuide