Margaret Davis has explained it exceptionally well, but a word of caution. The term Step-brother, or Step-sister is a relatively new term. It was not used in early records I have ever seen. Often a step son or daughter was referred to as a son-in-law, that term could mean either a daughters husband or a step son, very interchangeably. There just were no set rules for relationships until fairly recently. The terms used were often regional, or even family orientated, so always be careful in interpreting them. Margaret Behnke