I'm shuffling this story into chronological order, now that it's finished. This story covers the period from Abraham's death until Arthur locks Alucard up, including the series of Masters he went through and both World Wars.
Here's a quick who's-who. Figure Dracula, published 1897, occurred in the last decade or two of the 1800's. Next generation was around about the turn of the century or a little before, and the grandkids arrived by about WW1. Masters of Alucard show up in ALL CAPS.
First Generation, featuring the characters from Dracula
ABRAHAM x Mary Hellsing
1. BEATRICE
2. JOHN and PAUL (twins)
3. Rachel
Arthur x Constance Holmswood
1. Josephine
2. Byron
Mina x Johnathan Harker
1. Robert
John Seward X ? (read Unpredictable and find out!)
No children
x x x x x x
Second Generation Hellsing:
BEATRICE Hellsing x Harland Whitford, they had VICTOR, no other surviving children.
Robert Harker x Rachel Hellsing, they had ARTHUR and then much later Richard. Yes, THE Arthur.
JOHN Hellsing didn't have kids. At least, not that anyone knows about. We hope.
PAUL Hellsing x Josephine Holmswood. Two daughters, not named.
There were a lot of other kids involved, esp. in the grandkid generation and a handful of great-grandkids. But no one that comes into play and actually gets a name.