Hmm...
The Last Byzantine Emperor, Constantine XI, has one daughter, Magdalena, of whom I can't find any mention anywhere else aside from info from Constantine XI.
Constantine had 5 brothers: John (childless), Theodore (1 daughter: Helena and maybe more), Andronicus (childless, became a monk), Demetrius (1 daughter: Helena) and Thomas (2 daughters, 2 sons: Helena, Zoe - later Sophia, Andreas and Manuel).
Three Helena's are stated as descendants, aside from Sophia, Andreas and Manuel:
- Helena, Theodore's daughter, married John II of Cyprus. They had one child:
> Charlotte of Cyprus, who inherited her father's throne and died childless.
- Helena, Demetrius' daughter, married Mehmet II and had no known descendants.
- Helena, Thomas' daughter, married Lazar Brankovich, Despot of Serbia, before being annexed by the Ottoman Turks.
- Zoe/Sophia, Thomas' other daughter, became Grand Duchess of Moscow as Ivan III's second wife.
* Although Ivan and Sophia had children, Sophia's last known descendants perished in Russia during the Time of Troubles (1600's).
- Manuel, Thomas' younger son, lived a comfortable life in Istanbul, but not much is known about his two children: John and Andrew.
- Andreas, Thomas' elder son, became a de jure Byzantine Emperor with financial help from the Pope. He sold his 'title' to France's Charles VIII in 1494, but Charles dies only 4 years after. Andreas died in 1503, but named the famous Catholic Monarchs (Ferdinand II of Aragon & Isabella of Castille) as his heirs in his will.
According to Wikipedia, "Thomas Palaelogus' male-line soon went extinct."