How long have the other 2 been flowering for? maybe its a strain thing? Any light leaks? there could be a reason as to why 2 of them are staying in veg so check those problems.
How long have the other 2 been flowering for? maybe its a strain thing? Any light leaks? there could be a reason as to why 2 of them are staying in veg so check those problems.
Were they moved and replanted to be flowered? If so, a couple may have been shocked more than others and just be a bit behind. If they aren't showing sacks yet, then it is a good thing!