stepbrother C2+

/ˈstɛpˌbrʌðɚ/ a son of one's stepparent by an earlier marriage

stepchild C2+

/ˈstɛpˌtʃaɪld/ a child of one's spouse from a previous relationship

stepdaughter C2+

/ˈstɛpˌdɔtɚ/ a daughter of one's spouse by a former partner

stepniece C2+

/ˈstɛpˌnis/ a niece by marriage; the daughter of a stepsibling

stepsister C2+

/ˈstɛpˌsɪstɚ/ a daughter of one's stepparent by an earlier marriage

stepson C2+

/ˈstɛpˌsʌn/ a son of one's spouse by a former partner