If I had those, here's what I would do:
First, for both an optional but nice quality of life improvement would be to replace the HDDs with SSDs. Boot up and file access times will be much snappier.
Mac Mini
Congratulations! You have a nice foundation for a home server running linux. You could plug in a USB RAID of some sort ( example) and go full pirate running the *arr stack. You could set it up as a HTPC using the IR receiver with Kodi and whatever adapter is needed for your TV. You could set up a developers server, running git and whatever tool you find useful. You could set up https://nextcloud.com/ and self host most of the necessities of modern productivity. Or all of the above.
HP Pavilion G7
Congratulations! You have a great dedicated low-distraction writing and working machine. I have a pair of similar, though slightly lower end, laptops. I got a replacement battery for one of them from Ali, and run a minimal Debian + i3 setup on it. It's great for taking with me to write, whether code, gaming notes, creative writing or whatever else. The modern web is pretty terrible on it, which takes away a ton of distractions, but still usable enough if I need it in a pinch. I also have it set up for music, both local mp3s and streaming from my home server. It also runs a ton of classic games through DOSBOX. My other one I use as a sandbox, testing out alternative OSs, weird setups and whatnot. I haven't upgraded its HDD or battery yet, but my older daughter is wanting to type more when writing due to being left handed, so I'm thinking about setting it up as a dedicated machine for her.