There is a mother and a father还是There is a mother and father ?

There is a mother and father 。
表示一家。

There is a mother and father 。正确，mother和father这两个宾语可同用一个冠词a .

都可以

如果是夫妻， 就是There is a mother and father

如果不是夫妻（一个人的妈妈， 另外一个人的爸爸）， There is a mother and a father

There is a mother and father.