The Narrative Explanation of Inventory

Well Pyro has a Glassman wife so I guess they both use portable mirror passageways which are connected to their lodgings to grab the necessary item/s that they need for the occasion.

If I’m interpreting their gestures correctly, so do they.

I assumed most characters would just store their piles of stuff in their many unused houses. But how do you explain being able to play both a rubbery euphonium and an amber cello at the same time?

[quote=Captain Kaladin]I assumed most characters would just store their piles of stuff in their many unused houses. But how do you explain being able to play both a rubbery euphonium and an amber cello at the same time?[/quote] with skill obviously

They are rubbery/. They play themselves.
Yes, each other.

Given what slot the Rubbery Euphonium occupies, I always assumed it is sentient to an extent.