Question

this is her father and mother为什么这样用？

Answer 1

应该用these are his father and mother

Answer 2

1.This is her father and mother意思是这个人既当爹又当妈。隐含意思是一个人带大孩子。
2.但这种表达方式存在问题，this自身很少指人。用this person或this people更为恰当。
3.例句：
（1）她则对他们说，我的生命中不想再要别人，孩子们可以叫我爸爸或妈妈，我既当爹又当妈。
'I don't want anybody else in my life,' she tells them. 'the children can call me Daddy and Mommy. I am both.
（2）23年前，我的母亲去世了，抛下父亲一人抚养起一个14岁的女孩和一个11岁的男孩，他一下子扮起了既当爹又当妈的角色。
Twenty three years ago, my mom died , and this man was left all lone to raise a four teen years old girl and eleven years old boy. He suddenly had to be mom and dad.