Yes. Logically. He is a demigod, which means he's mortal
he was mortal
His mortal sons were Theseus, Pelias, Neleus and Hippothoon.
He was the son of Poseidon and a mortal woman.
His sword and sandals.
Yes she was, at least she was born as a mortal child. Maybe Dionysus made her immortal when he found her when Theseus left her behind on an island
All but Hercules. After he completed his 12 Labours, he was granted immortality.
no, he was a mortal just like most of the greek's heroes.
Given that his mother was Aethra, who most recount as mortal, and he was fathered by both Poseidon the sea god and Aegeus, yes.
He had a daughter named haploids and a son named Adrift.
Theseus had two fathers, Aegeus (a mortal) and Poseidon, both of whomhad lain with Theseus' mother Aethra in the same night.
Any son of Poseidon and a mortal woman is a demigod, as Polyphemus, Orion and Theseus. They did not belong to the sea. God of the sea - yes. Demigod of the sea - no.
Aegeus was not a God: but a mortal King, the father of Theseus.