The story of Katherine's paternity was apparently told to Robert Golden as well. This has come up on other news threads before as well as the fact that it was apparently confirmed by Queen Helen. I think the fact that a) Tino had a mistress b) the fact that Katharine looks so different and c) the age gap (9 yrs?) between Katharine and her next sibling has led to questions.
As for Paul, I don't know. Couldn't the fact that he was larger be a confirmation that he was Tino's? Tino as well as Greek George were very large while Nicholas, Andrew and Christopher were all slighter. Wasn't Alexander pretty large as well?