So its a case of it not working on irrational numbers, its just that we cant prove it because we cant calculate the multiplication of 2, right?

The issue is the proving part. We can't use repeated addition trickery (at least not in an obvious way) to show a product of two irrational negative numbers is positive. It's definitely still true that a product of two negative numbers is positive, just that proving it in general requires a different approach.

Somehow, my mind has issues with the e*pi = ke. Id say that ke = e * pi is impossible because k is an integer and pi isnt, no? It could never be equals, i think.

Yes this is correct. The ke example is for a proof by contradiction. We are assuming something is true in order to show it forces us to be able to conclude something ridiculous/false. Since the rest of our reasoning was correct, then it must have been our starting assumption that was wrong. So, we have to conclude our starting assumption was wrong/false.