The number of brothers and sisters is really very varying and sometimes lack of explanation creates real plotholes.
In LBT 6 Ducky mentions to be one of 13 twins. We saw that there were less in the original movie, but from her LBT 6 point of view I don't suppose Ducky would be exaggerating a fact which her friends can check out so easily. Her words "at the same time" rule out the possibility of her having included her later siblings in the term twins. We never ever saw 13 of them. I am quite fond of the idea of a story about Ducky and one sister of her looking absolutely identical... Double Ducky so to speak.
Were there less in the original movie? I'm sure Ducky would know how many siblings she has. But is it possible "twins" could mean something different in the LBT world? That would include her later siblings!