Hi ! So, one of them I've noticed will not be possible to unlock until I apply a fix to the game. Fortunately that fix will be compatible with previous saves.
SPOILER AHEAD
Once the 1.25a is out, all you need to do is use Rohan on the cocoon hanging from the ceiling in the Guards Quarters. That will require Rohan to be aware to some capacity he made the fungus and having been calmed down by the player. Best way to do that is to start small and have him inspect the fungus pod he's made in the cells.
The one you have already is a result of having both Anthony and Cyril at the same time in your companions, since Daagün is the father of Cyril and Cyril's recommended him to Anthony, that will trigger the memory.
For the third memory, you will need to have Rohan recognise the fungus as his creation.
On that note, I will take your advice and make better hints in the Memories screen.
Thank you for liking the game and taking the time to give me your feedback.