Something that may be of help with the litterbox issues is to take one of the kitten's stools and place it in the box on top of the litter. This seemed to help them know where to go. I, along with my mother, have recently raised a litter of orphaned kittens from approximately 1-2 days of age to their current age of 3 months. She would nurse them while I was at work and I would take over during afternoons, evenings, and weekends. From your post, it seems that the kittens already were pretty good at using the litterbox at their previous home. But for me, this really helped with litterbox training.
It is hard to say when they will really interact with humans. You figure that my litter was hand raised, bottle fed for all but the first day or two of their lives. So they are already used to human contact. That said, they still like to explore and go off and do their own thing. It is just part of their nature. Yet when I get home to see them, they come running out of their room to see me!
In your case, they probably will be similar. They will go running off to play and after a while, they will come to you. But hold them as much as you can without them getting squirmy. If they squirm to get down, let them down. But hold them as much as you can as I feel that will help acclimate them to you.