MorpHDoc

I don't think it's a mistake. Books and show have differences, and your link is for the show and only the show. There is a difference regarding how many daughters Oberyn and Ellaria have: show 5/books 4. Tyene is not Ellaria's.

No, but in the TV show Doran says "4 nieces" but the wiki for the TV show says they have 5 daughters. Hence the wiki must be wrong and the show is correct and in line with the books.

In the books?

According to this link, http://awoiaf.westeros.org/index.php/Oberyn_Martell, Oberyn and Ellaria have 4 daughters. Elia, Obella, Dorea, and Loreza.

Yea, In the books.

Sorry, I used this source http://gameofthrones.wikia.com/wiki/Ellaria_Sandwhich clearly states she has 5. I guess it's a mistake on that wiki.

However, in the show Tyene calls Ellaria "Mother", but in the books she's the daughter of a septa.

Can someone answer this question:

How many daughters does Elleria has with Oberyn? I thought it was 5, but Prince Doran said "you are a mother of four of my nieces". Mistake? I know it's probably not relevant in a grant scheme of things, but I just wanted to know.