Having siblings was very important back then. Having parents and grandparents and siblings all living in the same household was common. The more people you had in the household to share chores (like gathering food, preparing food and working for money or barter), the easier your life was. So having brothers and sisters was good.
If you were a girl, having at least one brother was even more important. Under Norman law and custom, girls needed men to arrange their marriages, make legal contracts, arrange their entry to a nunnery, and help them protect any possessions (land, animals, or riches). Your father would protect you and care for you as long as he was alive.
But back then the life expectancy was not as long as now. So you needed a brother to continue protecting you after your father was gone, and perhaps after your husband was gone.
In “Precious Norman Honor” Aethel has good future prospects. She has her great-uncle Wulfstan, who is man-at-arms to an Earl, to arrange a marriage and she has her brother Bert. She and he may not get along, but both of them realize that they are Family and have obligations to each other.