My little girl was 3 and a half when took away the dummy, and we felt it was the right time as it was becoming a real problem, in that she would have it ALL THE TIME - if we forgot one, we'd have to go home and fetch it and buy another one. She simply wasn't ready beforehand too. (when we did give the dummies away, we gave one as a gift to a friends new baby and the others we prepared a special box and decorated it over a few days, and then left her dummies in there for the dummy fairy who took them and left a present).
I think as you say, you have another baby on the way which is going to be huge in her little World, and if she needs comforting, and you're going to need things to be as easy as possible when the new baby arrives, i would go with your gut and leave her with the dummy for now.
Try not to cave into the peer pressure from family, as hard as that can be - but maybe tell them if you can, quite firmly, you need to do what you think is right and it's not up for discussion.
But when you come to get rid of them, that's a whole new ball game of stress, which i don't reckon you need right now! Hope this helps.