If you had twins your body would make enough, and it would only know it had to feed twins at the point they were born and you put them both to the breast. Since you've been BFing DS#1 all through the PG i'd imagine that your body will make plenty of colostrum and plenty of milk. Babies that do not get "enough" colostrum don't exist anymore- in the 70's they used to get mums to express off the colostrum and give bubs formula until the "real" milk came in - THOSE babies didn't get enough colostrum!

I would say the usual baby-to-breast formula will ensure there's plenty of milk for both kidlets (by "baby" i just mean whichever of your boys happens to be hungry!) since it's time at the breast that brings supply in and dictates the production level. If both boys feed there will be enough for both boys.

FWIW colostrum is present to some extent in breastmilk for the first 6 weeks - plent of time!

Don't fret

Bx