Sergei Orlov was born to Dmitri and Anastasiya Orlov. The couple both attended Hogwarts and had been childhood friends growing up in same neighborhood in the Russian Yukon. However Dmitri did not handle the stresses of being a father well...
He started drinking heavily, but nothing bad had come out of it... yet. Anastasiya became pregnant again about a year after Sergei was born. Sergei was barely two years old when his younger sister, Arina Orlov was born. Unfortunately the birth of Arina made Dmitri drink more and now he started staying late out at night and yelling at Anastasiya when he thought the kids were asleep. This staying out at night led Dmitri to sleep around... and nothing good came out of that let me tell you.
When Arina was a year old Anastasiya became pregnant again by some miracle... however there was another surprise for the Orlovs. Someone left a baby boy at their doorstop claiming that the father was Dmitri. Blood tests confirmed and the mother was never found. The boy's name was Andrei. Nine months later Anastasiya's last child (with Dmitri) was born. Another girl named Iona.
Now Anastasiya despised Andrei as he was a constant remainder of her husband's antics. Which he hadn't stopped by the way, if anything they got worse. The yelling between Dmitri and Anastasiya got worse. Luckily the Orlovs were a wealthy family and lived in a very large house... but soon all twenty-four bedrooms would be needed.
When Dmitri was four years old two more surprises arrived on the Orlov doorstep. Two more kids, a boy and a girl named Aleksander and Sabina, and no they were not twins... but they shared a birthday. Use your imagination. Anastasiya as one can imagine was furious with Dmitri and things only got worse from there. However if there was one good thing about Dmitri... he never laid a hand against any of his children or his wife.
More children kept arriving. When Dmitri was five three baby girls arrived on his door step. They were triplets this time. Rose, Selena and Stasya. Meanwhile Anastasiya had basically given up on hating Dmitri's children... she still hated Dmitri but she started caring for all the children as if they were her own. In fact they're the only reason she stuck around.
When Dmitri was 6 more children arrived. Once again they were in a pair, and once again they weren't twins and shared a birthday. It was two boys this time. Igor and Nazar. Six months after that another set of twins arrived. A boy and a girl named Nika and Katya. About nine months after the arrival of Nika and Katya another boy arrived. His name was Stepan.
At this point Anastasiya need some love so she started sleeping around as well. Eventually she got pregnant and when Dmitri was 9, she gave birth to a baby girl. The girl's name was Eva. However Anastasiya gave her the last name Dragomirova, as that was her last name. During this time two more children sired by Dmitri arrived. Two girls named Marina and Sonya.
Anastasiya and Dmitri continued to sleep around and by the time Sergei was 13 he had 6 more half-siblings. His mother had four more girls named Vasilisa, Veronika, Viktoria and Zhanna. Dmitri had two more boys named Viktor and Vlad.
Now since Dmitri and Anastasiya were such crappy parents most of that burden fell on the shoulders of Sergei, Arina, Andrei and Iona. Luckily for the kids, the four took the responsibility seriously and did fine at the job. Sergei took on a job soon as he could to help bring in extra money. He worked at a Quidditch shop.
Quidditch has been one passion of Sergei's that's been constant. He's always enjoyed playing Quidditch and is an excellent keeper. Arina plays Chaser and Iona plays beater while Andrei's seeker. The four of them are very close as they have to basically run the family while their parents screw around. In more ways than one.