Vedas do mention Mahabharata character as according to tradition in previous Yuga only 3 Vedas were present and that too only samhitas.
Atharva veda was compiled after Mahabharata that's why in oldest part of Mahabharata (Sanjaya conversation including bhagvad geeta) you'll only find mention of 3 Vedas and in ramayana too only 3 Vedas, the four priest yajna(acc 4 vedas) for once was started by janamejaya the son of parikshita. This is why the oldest part of Mahabharata and ramayana only mention 3 preist yajna(acc 3 vedas)-
- parikshita (son of abhimanyu)
Listen to the good praise of the King belonging to all people, who,
(like) a god, is above men, (listen to the praise) of Parikṣit! -
‘Parikṣit has just now made us peaceful dwelling; darkness has just
now run to its dwelling.’ The Kuru householder, preparing (grains) for
milling, speaks (thus) with his wife. — ‘What shall I bring you, sour
milk, the mantha [a barley/milk drink?' the wife keeps asking in the
Realm of King Pariksit. — By itself, the ripe barley bends heavily
(iva) over the deep track of the path. The dynasty thrives
auspiciously in the Realm of King Parikṣit.”
Parikshit is eulogised in a hymn of the Atharvaveda (XX.127.7-10) as a
great Kuru king (Kauravya), whose realm flowed with milk and honey and
people lived happily in his kingdom. He is mentioned as the raja
vishvajanina (universal king).
You can read more here
jaimini student of bhagvan ved vyasa has a shakha of sama Veda and brahmanam named after him
When Rishi Veda Vyasa divided ancient Vedic hymns into four parts
based on their use in the sacrificial rites, and taught them to his
four chief disciples – Paila, Vaisampayana, Jaimini and
Sumantu, Samaveda was transmitted to rishi Jaimini. "He divided the
Veda into four, namely Rig, Yajur, Sama and Atharva. The histories and
the Puranas are said to be the fifth Veda."
- Brahmanda Purana 1.4.21
You can read more here
Out of 1000 Shakhas of Samaveda only three Shakhas are
surviving. Kauthuma Shakha, Jaiminiya Shakha and Rananiya Shakha
Anyway if I keep writing the name of all rishis who were student of bhagvan vedd vyasa and are named in Vedas a very long list will be There, so instead
You should read the list of names of different shakhas of Vedas you'll be surprised too find mentions of all relatives and students of ved vyasa-
Here read the blog here: https://googleweblight.com/i?u=https://animeshnagarblog.wordpress.com/2015/06/23/a-list-of-hundred-and-one-yajurveda-shakhas/&hl=en-IN
You'll find names of shuka, apasthamba, bodhyana, parashar etc.
Whole family tree of parikshita is mentioned in brahmanas of vedas- including his son and grandson- janamejaya 1 and janamejaya 2
Then rishis like shaunaka, ashvalyana, the other students of ved vyasa are also mentioned they were present during Mahabharata and they wrote the shrauta sutras of Vedas as well as vedangas
Krishna is mentioned in chadogya upanishad.
Janaka king of mithila is mentioned in multiple upanishads