You are wrong. While Bhrgu and Angira are the oldest, Atri and Vasishta thereafter followed.
You know Aatreya, I do not make an assertion if I do not have the proof. And Lokmanya Tilak Maharaj is always there with me to help. Lokmanya always mentions his sources from Vedas, Brahmanas or Aranyakas.
"The RigVeda mentions a number of ancient sacrificers styled “our fathers” (II, 33, 13; VI, 22, 2), who instituted the sacrifice in ancient times and laid down, for the guidance of man, the path which he should, in future, follow. Thus the sacrifice offered by Manu, is taken as the type and other sacrifices are compared with it in I, 76, 5.
But Manu was not alone to offer this ancient sacrifice to the gods. In X, 63, 7, he is said to have made the first offerings to the gods along with the seven Hotṛis; while Angiras and Yayâti are mentioned with him as ancient sacrificers in I, 31, 17, Bhṛigu and Angiras in VIII, 43, 13, Atharvan and Dadhyañch in I, 80, 16 and Dadhyañch, Angiras, Atri and Kanva in I, 139, 9.
Atharvan by his sacrifices is elsewhere described, as having first extended the paths, whereupon the sun was born (I, 83, 5), and the Atharvans, in the plural, are styled “our fathers” (nah pitarah) along with Angirases, Navagvas and Bhṛgus in X, 14, 6. In II, 34, 12, Dashagvas are said to have been the first to offer a sacrifice; while in X, 92, 10 Atharvan is spoken of, as having established order by sacrifices, when the Bhṛigus showed themselves as gods by their skill.
Philologically the name of Atharvan appears as Athravan, meaning a fire-priest, in the Avesta, and the word Angiras is said to be etymologically connected with the Greek Aggilos, a “messenger” and the Persian Angara “a mounted courier.” In the Aitareya Brâhmana (III, 34) Angirases are said to be the same as Angârâh, “burning coals or fire,” (Cf. RigVeda X. 62, 5).
Whether we accept these etymologies as absolutely correct or not, the resemblance between the different words sufficiently warrants the assumption that Atharvan and Angiras must have been the ancient sacrificers of the whole Aryan race and not merely of the Vedic people. Therefore, even though Manu, Atharvan, Angiras be not the names of particular individuals, still there can be little doubt that they represented families of priests* who conducted, if not originated the sacrifices in primeval times, that is, before the Aryan separation**, and who, for this reason, seem to have attained almost divine character in the eyes of the poets of the RigVeda."
* In the same way as I may be a Vasishtha.
** According to Tilak the separation (between the West going Aryans and the rest) occurred around 3,500 BC.
