Custom validation for reactive forms, Validators for two nested inputs,

I have two input boxes, start date and end date,
when data in entered, both the values should not be the same, I need a validator for that

then there is an add button, which when clicked adds two more input boxes, these two start date and end date, should not match the above input boxes days
Like the example in the photo, skill and exp are my star date and end date respectively

I am having difficulty writing custom validation for it.

example
https://stackblitz.com/edit/angular-u8dxok?file=src%2Fapp%2Fapp.component.html

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