At that age, they do not need a 'party' party.
MANY of my friends, do not have 'parties' for their kids, until they are in school or 5 or so years old.
At that age, they will enjoy it regardless... and in fact, the smaller the group... the better. Less chances of the child getting over-stimulated and fussy/tired.
At that age, its fine to just have family... and decorate your home with balloons and streamers... and get her a cake. And her favorite food item.
that is what we did for our kids as well, at that age. Our kids LOVED their Birthday. And of course, opening presents. Which we hid around the living room like an Easter Egg Hunt. It was just me, Hubby, our kids and Grandma and an Aunty. And our kids LOVED it and felt special.
That is all you need to do.
Plus with 4 week old babies... well, I wouldn't want to take them out amongst tons of people, yet.
all the best,
Susan