I have never reach to the fifth generation in the sims 3 The idea of their name: Arabic "one" > Wahid Arabic "two" > Ethnan > Wathnan Arabic "three" Thalatha > Walatha Arabic "four" > Aluba > W...
On the subject of family trees I just thought to mention, for those who might be interested, that MCCC provides the facility to export a Sim's family tree in standard gedcom format for genealogical software. I've tended only to play single Sims so do not have any personal experience of using gedcom but it might help keep track of large family trees.