From the pictures I would say that they are not Bristlenose and they aren't albino either. This could just be from the pictures but they look nothing like any albino I have ever seen and at 3-4 inches they should have distinct barbels already. Might be a different species of albino but I don't know.
Check those images out and see if they even come close. I could not find a BN that matches your pictures.
The 3 BN plecos I had in the past were under 3 inches when I got them, 2 males and 1 female and they had very distinct bristles already and were very easy to distinguish male from female.