Dostoevsky has 4 brothers born to a sort of nobleman and they go on to become a nihilist, a soldier, a priest, and a cripple. I didn't realize it till now, but thats basically the same expectations the sons of a king would have.
The firstborn would inherit the estate of his father completely, and become a nobleman himself. The second son would join the military, and the third would join a monastery since the only thing left he could receive was an education. The fourthborn son would get so little, maybe some clothes and a horse, all he could do is travel from monastery to monastery, since the priesthood was the only institution willing to feed him for nothing in return. He would have to live off the generosity of his third brother as he would never reconcile himself to becoming a serf.
Dostoevsky recreated this institution inside one family, with some minor changes. His firstborn was in the military, but the forth brother, the sick one, was alive through the generosity of a serf family, they were childless and saw any child as a gift from heaven, their motivation was religious, and still conformed to him being alive through the generosity of his Third brother.
Why did he write it this way?
I have some answers ruminating now, but I want to hear what the rest of you think.