In Between Prey: when to offer multiple prey items

[DestinyLynette]

So, of my snakes, I have one big adult who wolfs down rats, and then a bunch of babies- a '13 bee, a '12 pastave, '12 wildtype, etc. And a rogue adult pastel who is on a hunger strike and won't eat anything offered. Now, my question:

The place I get my prey from (I only feed live), they only have mice (hopper - adult, occasional pinks) and rats (med-x-large, maybe a small, but never pups). In my fantasy world, I feed my smaller ones pups, but sadly they're not available, so they get adult mice. I'm wondering, at what weight range would you suggest offering an adult mouse plus something more, and what that something more would be. My pastave *could* take down a small adult rat now, but it's very uncomfortably big. And I feel like she is probably between mice and rats right now, but I may be wrong.

Anyways, input appreciated! Feeding day is tomorrow, so I wanted to know before.

Edit: Oh, and the new weight on Rosca is over 2700g; would you move her to something bigger than a med rat?