No they can't really "hog" the milk as she should have enough teats available to nurse them all at this point. As they outsize their litter mates though they are more likely to push them away a bit but the littler ones should still be able to get sufficient milk if she's producing it. When you check her belly do you see her teats exposed (from the action of the pups nursing on them)?

You could try removing the 2 big pups to a warm spot for an hour or two a couple of times a day to try and allow the smaller littermates access to mom without competition. You'd have to make sure the bigger ones have a warm spot with bedding and I'd only pull them for a short while a couple of times a day to see if it made any difference.