Generally the ribbing is done on the smaller needles, so switch to the larger ones when you're done with it. Older patterns may not have specified that, everyone 'knew' when to switch.
You have 4 sts on the holder/pin and pick up another 4 sts so you have 8 total (for that size), then you arrange them on the dpns to work in the round. I'd just leave them on 2 dpns and use a 3rd to knit with because it's a lot easier to handle than 4 needles.
sue- knitting heretic