Who are they? Any ideas?

Meritaten Tasherit and Ankhesenpaaten Tasherit were the two youngest Amarna princesses. It is almost certain that Meritaten Tasherit was Meritaten's child (born in the 15th regnal year of Akhenaten) and A. Tasherit was Ankhesenpaaten's (born in the 17th year), but nobody knows who was their father. It is usually believed that the father was Akhenaten, marrying his eldest daughter Meritaten first, fathering a child, then giving her to Smenkhkare and marrying Meketaten who dies in childbirth, then marrying to Ankhes. (I think this theory is a little far-fetched. Why can nobody assume that Meritaten's daughter was simply Smenkhkare's child? There's no evidence that Akhenaten married any of his daughters.) As for Ankhesenpaaten Tasherit, she was unknown for egyptologists for a long time, the only evidence revealing her existence was found only in 1938. Her only importance is that she helped to find out how long was Akhenaten's reign (Ankhesenpaaten, who was born around the 5th year, couldn't reach child-bearing age before the 17th year.)
It seems that both princesses died young, for there are no further informations about them.

Yes that is what I have always been lead to believe and is the theory I still follow. I should point out however the opinion of someone I read about in a book. Can't remember who it was but they thought that just because the two princess had the name 'Tasherait' didn't mean they were the daughters of the elder princess. They believed they could just as easily have been younger Amarna princesses of the same name but were living at the same time as Meriaten and Ankhesenpaaten so were given the epithet 'Tasherait'.

Yes, but I've heard it was a custom to give this epithet to a girl if she has the same name as her mother; just like Neferneferuaten Nefertiti and Neferneferuaten Tasherit. (I wonder whether this theory is based only on these three examples...)
The Hermopolis talatat, which was found in 1938, clearly identifies Ankhesenpaaten Tasherit as Ankhesenpaaten's daughter. (It may seem wild, since she was about 12 yrs old but at that time girls were considered grownups by that age.) I've read that Meritaten Tasherit always appears together with Meritaten. I guess it means that Meritaten was the mother.

Oh I totally agree. I think that they were indeed the daughters of Meritaten and Ankhesenpaaten but I just thought i'd mention the theory. Will have to check out this Hermopolis Talatat because, much as we have always assumed they were the daughters of Akhenaten's 1st and 3rd daughters, i'd never seen or read anything that prooved it conclusively.

So did any of the daughters live to see Tut's reign? Is there any proof?
it seems so odd that almost everyone died except Tut and his wife. So Ankhesenpaaten had a daughter? I'm guessing by her father. It would seem that both tries with Tut failed.

Well Meketaten died in childbirth and we assume Meritaten died aswell. No one knows for certain what happened to the younger three; Neferneferuaten Tasherit,Neferneferure and Sotepenre.Have heard some rumers that one of them may have married a foreign king but their just rumers.

Meritaten and ankhesenapaaten- Tashet? they were ankhesenamun's sister, and daughter.