I want to pair two pairs (4 hearing aid pieces)to my iPhone 13 is it possible ?

My answer would be no, but what brand and model of hearing aids do you wear? Also, if I can ask, why would you want or need to have all 4 paired with your phone at the same time?

You could do what you are wanting but you would have to "Forget" each set, reboot your iPhone and then pair the second set which is totally possible. It is a tedious solution but it would work.