plush vine
I feel like giving the twins the ability to read a book (newly published) would be a good benchmark for memory upgrades. Since if they can remember the relevant parts to understand the story, including between streams, that would likely be a very good measure for making them more lifelike.
The they would be able to:
flip pages forward and back
flip to specific pages
Put a bookmark
Open and close the book at will
It would be something for them to do when bored or to ignore you for the funny. And you could even have a glasses and book png appear on them when it’s open.
native summit
flips back and forth over the same page