The date of Tarondor's birth appears only in The History of Middle-earth volume XII, The Peoples of Middle-earth. It cannot therefore be considered completely reliable.
2
Tarondor's name is not explained, but it appears to be composed of the elements Tar- 'high king' and -ondor a variant form of Gondor, 'land of stone'. Somewhat confusingly, there was also a King of Arnor named Tarondor, but clearly the Gondorian connection cannot apply to this northern King, and his name apparently had the more general meaning 'king of stones'.
3
In volume XII of The History of Middle-earth, Tarondor is referred to as Minastan's eldest son. That implies that he had at least one younger brother, and probably other siblings as well.