they are my mother and my father,还是it is my mother and my father

正确写法是：
They are my mother and father.

如果有更多的人在场，需要指明哪一位，那么也可以说：
This is my mother, and this is my father.
The lady there in red and black is my mother. And the gentleman over there in blue and white is my father.

标准说法是 They are.
口语可以用 it's.

另外，还是用 They are my parents 更英语化些。

不要把爸妈当牲畜了，用it来介绍...
他们是我的爸妈，用前句
我爸妈干这个，用后句，当然句子还不完整
这里不赘述了
准确的介绍当用
These are my parents .