What are the consequences of brothers and sisters sleeping together for a long time?

As long as they are of the opposite sex, they must sleep in separate beds before entering puberty.

Family, brothers and sisters, blood relationship, etc. It's just a taboo in people's consciousness. But the mutual attraction between the two sexes is based on matter (endocrine), which is primary and consciousness is secondary. Therefore, before entering adolescence, brothers and sisters must sleep in separate beds. It has nothing to do with whether they have twins or not.