Can you? Hand Crossbows have the "Ammunition" property, which means you need a free hand to load them. You get one free-object interaction per turn, so:
Turn 1: Both crossbows are already loaded, so you can fire both. As a free object-interaction you stow one of them.
Turn 2: You fire your equipped hand crossbow (loading it with your free hand), then free-item-interaction draw the second. However, it is unloaded and you don't have a free hand to load it, so you can't fire it.
Similar with shield, but (de)equipping a shield is a full Action, so it works even less well.
I suppose (really, it's just my wild guess) that since a hand-crosbow doesn't require 2 hands to align it like other crossbows, which you're also loading every round while also carrying them with 2 hands, and it's not very powerfull, you're expected to be able to load it just with 2-3 fingers of you second hand, and that doesn't mean you need to put anything away from that hand.
