I'm not so sure... thingol had been in Aman, so may be considered eldar, and married a maiar... and Tolkien's statement is clear:
"There were three unions of the Eldar and the Edain: Lúthien and Beren; Idril and Tuor; Arwen and Aragorn. By the last the long-sundered branches of the Half-elven were reunited and their line was restored."
(Google Miracoulus)
but yes, surely their heirs were sindar