i haven't had the opportunity to deal with both kiddos at once, but i am in the middle of pregnancy number 2. i was quite worried when i got pg about my very high demanding nurser. he nursed every 2 hours, day and night.
what has happened as my pregnancy progressed is that he has cut back his nursing tremendously, on his own. there has been no trauma, no tears, no frustration, etc.
i think i was around 17 weeks pg when he went from the every 2 hour thing to a few times during the day and not nursing at all at night. now he nurses for a couple minutes at nap and a couple at bedtime. he would probably nurse more at these sessions, however it is really painful right now so i limit them. which, oddly he is fine with too.
your dc1 is a little younger then mine (who will be 24 months when baby arrives), but he may surprise you.
congrats on your pg!