“直系亲属关系”常见的英文表达是 “immediate family relationship” 或 “direct family relationship”。
immediate family relationship： “immediate family” 是一个常用短语，指直系亲属，包括父母、配偶、子女、兄弟姐妹等，“immediate family relationship” 自然就表示直系亲属关系。
direct family relationship： “direct” 有直接的、直系的意思，“direct family relationship” 同样传达直系亲属关系这一含义。