Since I can only post here for the meantime, here's an update on my re-potting.
These 2 cacti have grown together for years, untangling their roots was a huge pain but they seem happy now!
Drying out the fruits to collect seeds, bought more tiny pots tonight so hopefully some seeds take and I can log them!
Still need an ID on Willis, the taller white-spined cactus. Agustus is a mammillaria prolifera I believe.
Thanks and happy farming.