15 month old twins and 3 months pregnant. How to keep my twins from picking on newborn after it arrives?

My twins always take toys and such from each other and haven't understood sharing yet. I'm afraid they might start taking pacifiers, toys, etc from the newborn when it gets here, probably not to make it cry, but just because my twins are "selfish" as far as babies go. You know how babies don't understand how to take others feelings into consideration before they do or say something. Well on that topic my twins were 2 months premature and they don't talk yet, at all. My son "says" Dada, Baba. That is it. He blows "raspberries too. My daughter only says Dada (stretched out) but extremely rarely and blows "raspberries" and "sings". So I can't just explain to them not to do something. My son reacts to No, but my daughter doesn't. Anyway does anyone have any Good advice (nothing negative)? I'm really hoping to hear from mothers or fathers with twins and a baby(ies) around 2 to 3 years apart if possible.