Thanks for the replies, hadn't thought of the young bees building comb, it would certainly explain the activity in hive 2. The nuc hive does appear to have more bees that when I installed it so I guess just a matter of giving them time. There was brood emerging, watched one chewing its way out as we inspected and there was both larva and capped brood so queen is laying.
I guess it is just a matter of giving them time and letting them slowly build numbers up in the hive and they will build when they need more room.
Didn't see any evidence of ants on frames but there were still a few around even though I greased the stand legs and had stopped feeding. I'm guessing if they have been spending time defending the hive from ants it would slow them down with other activities like comb building and they would be reluctant to build more comb if flat out defending what they already have.
Think starting with 3 hives was a good move, after only a week I can already see differences in them. Looks like I will have one really strong hive so should at least have the ability to rob resources from it in a month or so if need to help out the other hives.