I use the same technique, however since my boys are tricky: I scoop the first and get him into the carrier, set the lid closed, and place something on top of it like a book. I dont lock it because I dont want to be fumbling with a latch while trying to get the second one, and usually the second chin is harder to get since he's been tipped off that theyre going in the carrier and I dont want the first one to escape in the meantime.
In scooping them up I sometimes get them into a corner of a shelf and with one hand block them from leaping away and the other hand scoop under the belly and supporting the feet bring towards me using the outside hand to hold them secure.