In the version that claims that Aegeus is his father, no.
However, if you accept the version that claims that Poseidon is the one that fathered him, then yes, Theseus has many, many siblings...
TN
She had a younger sister, Muriel.
Theseus got the sword from the rock that he pulled it from.From Ariadne
Theseis is the story of Theseus
Theseus killed the minotaur
Two women married Theseus. These were Hippolyta and Phaedra. Theseus did not have both as wives simultaneously.
They are Theseus' brothers.
Theseus
minosthe daughter of minos helped theseus defeat the monitaur
King Aegeus was one of the two fathers of Theseus. The other father of Theseus was the sea god Poseidon.
For love of Theseus.
Theseus was a legendary king of Athens.