In your culture, can you marry into a family in which a sibling of yours is already married into?
In my culture, it is seen as forbidden to marry into the same family as your sibling. No explicit reason is given for this, it is just seen as a taboo. I am of the Yoruba tribe in Nigeria.
Albeit, some argue that it is our belief that once a child marries into a family, the two families are automatically seen or believed to become one, hence, "you cannot marry from within your family".