If you really want to make them remember something, you can use the black magics of exporting and editing NPC Memories, then importing them back into the game.
I'd only do one or two sections in the advanced memories, and only simplified information about foundational stuff, like who your character is and why they came to Silverpine or that (NPC) is married with (your character) and (other NPC).
Downside is it's annoying to check up on the memories every session or two depending on how often you talk to the NPC. You'll have to monitor them to see if whatever memory is about to be forgotten and copy paste/swap the old memory with a newer memory. Then do it again for the other NPC.