37 weeks and still no name

Hi ladies,

I'm currently 37 weeks and 4 days pregnant with our baby, but we still don't have a name. In other words; we're a bit stressed. We don't know if it's a boy or a girl.

Half-sister is Isabelle Maria Aurelie, nickname Isa.
Half-brother is Valentijn Julius Alexander, nickname Tijn.
Sister is Katharina Phileine Eleonore, nickname Kate.
Brother is Sebastiaan William Andreas, nickname Seb.

And now for our last little miracle. We're looking for a name that fits with the names above, and mainly with Isa, Tijn, Kate and Seb. We want a long name and a short nickname derived from it.

If it's a girl, the second name will be Sophia and the third name Margot.
If it's a boy, the second name will be Benjamin and the third Reinier.
So for both genders, we still need a long, classic first name, and then a short nickname.

Hopefully you can help us, we're at a loss :/
Love, Valerie