Twins are unexpected, but surely they knew at least one child will be born? Even one extra is a huge commitment when you don't have the means.

Read the quote carefully. IMO it is not saying that the pregnancy was a surprise, but that twins was a surprise.

Which is exactly my point.

Twins are much more common among people using fertility drugs than the majority of the population; so if you are on those drugs, you might expect them.

P.S. not trying to be snarky, just thought it was an interesting fact