Congratulations to the happy parents!
I think that the male word for twins (jumeaux) would also be used if the sex was not known to the writer. If they knew, they would probably have mentioned it in the sex of the babies.
A.f.a.i.k. jumeaux are for two boys or a boy and a girl.
jumelles are for two girls.
I think that the papers had their information from sources close to the family and not officialy, from the Court.