Taking 1 big stroller that will be more difficult to shlep, open and close, but will be 1 piece. Or 3 smaller more travel friendly doonas and stroller but will be more strollers to deal with.
Some thoughts:
Do the newborns have booked seats?
Do you physically have enough hands to push 3 strollers?
How much traveling are you doing (ie multiple airports/trips)?.... Buggy board isn't helpful if 3 year old falls asleep