What is the relationship between half-brothers?

This is a brother-sister relationship.

Half-step relationship is a special family relationship. Two children have the same mother, but different fathers. In this relationship, two people are related by blood, so they are called brothers and sisters. In law, half-brothers and sisters are recognized as immediate family members, that is to say, they enjoy the rights and obligations related to immediate family members, such as inheritance rights and maintenance obligations.