Even if it's their father, mother, brother or sister who has died, they are not to make themselves unclean, because their uncut hair announces their dedication to God.
A priest must not make himself unclean by going near a dead body. However, if it's his father, mother, son, daughter, brother, or a sister that's not married, then he may do so.
However, there were some men who were unclean because they had been in contact with a dead body, so they could not keep the Passover on that day. They went to see Moses and Aaron the same day,