How to validate both fields at the same time when changing one of them, and only display error message if both fields are not empty?

[Hujianboo]

Hi~ I have one question. I have a situation: firstname and lastname can't all be empty.When all of them are empty,all fields show error,but when one of them is not emty, there are no error.
I use yup as validator util and react hook form to achieve it.
when all fileds are empty just like this

But When i change onevalue,the other's error is still existed

Only triggering the blur event of the other input by myself can make the error disappear.

How can i manually trigger specified field's rule when change it's dependencing field value?
This is code example :
example