应该用is,这句话可以理解成:“How is your mother and how is your father”的一种缩句形式。
应该用are。原因:复数用are,单数或第三人称用is。mother and father是两个人,爸爸和妈妈,所以是复数,应当用are。
是“How are your mother and father”?因为有爸爸,妈妈,两个人,所以是复数
肯定是are
父亲和母亲,两个人,当然用复数。How are your mother and father?