Formal sworn, should be in front of Mr. Guan, say together: heaven is above, the earth is witness, and now in front of Mr. Guan, XXX and XXX are willing to become sworn brothers and sisters of the opposite sex, sharing weal and woe, not seeking to be born on the same day in the same year, but seeking to die on the same day in the same year!
Then, send a big gift and complete the ceremony.
Since then, you have officially become brother and sister!