I didn't answer the poll, because in my case any answer from 2-6 is kind of correct.
I married a divorced woman in 1984 and immediately gained two teenaged step-daughters. They're now 58 and 56.
Then my wife and I had two boys of our own. (Her doctor recommended if we were going to have any kids ourselves we'd better do it quickly, as she was already 35 when we got married.) My biological sons are currently 41 and 40. (They're so cute at that age!)
Then my oldest step-daughter went through a messy divorce and asked us to raise her daughter (my step-granddaughter) until she could get back on her feet financially. So I raised a little girl from ages 4 to 8, and she became more or less the daughter I never had. (She still feels like my sons are her "older brothers," although they're technically her uncles, and they think of her as a little sister.) She's now 36.
And finally, my wife's brother and his wife found themselves unable to care for their son, so we raised him from when he was two and a half months old to the present. He's now 19, and he couldn't be any more my son if we did actually share any DNA.
So take your pick: 2, 3, 4, 5, or 6, depending on who all you want to count.
Johnathan