The Hamlet Project

Is Hamlet an only child?
If he has or had any sibling, they are nowhere to be seen in the play. We know he’s the only boy but does he have a sister stashed somewhere? Maybe married off to the King of Sweden or something?
Or did he have brothers who didn’t survive?
It is rare for a Royal family to have just one child. Part of the deal with having a Royal Family at all is to insure lots of heirs. So I’m curious about Hamlet’s only-ness.
I’m part only child (on one side) but no one’s concerned about middle class lineage.
And I am the sole daughter both of my mother – to whom I am also the sole child and to my father, who has two sons.
It never occurred to me to wonder about Hamlet’s siblings before – why he doesn’t seem to have any and what happened there.
Was Gertrude unable to have more? Did she become a little like Lady Macbeth and lose a child or two?
Are there sisters somewhere?
I’d like to imagine that there are three sisters and one is Queen of Sweden, another is in a nunnery (the one where Hamlet would send Ophelia) and the third has been discovered, since she ran off, joined up some pirates off the coast.
It’s a natural extension of Virginia Woolf’s imagining of Shakespeare’s sister – this extra fictional step of imagining Hamlet’s sisters. If I started a band again, I might call it Hamlet’s sister, since someone already took Shakespeare’s sister.
It’s the next best thing.