The duo from Ramayana can effortlessly squash Bhishma and Drona together single handedly. Both Indrajit and Hanuman have feats putting them above devas.
Indrajit had defeated Dev's and captured Indra in battle.
Having agitated the ocean of celestial hosts, having darts and lances for its fishes, showering arms for its moss, elephants for its tortoises, steeds for its frogs, Rudra and Aditya for its ferocious animals, the Maruts and Vasus for its mighty serpents, cars, horses, and elephants for its volume of waters, and infantry for its spacious shore, this one (Indrajit), taking captive the lord of the celestials himself, had brought him into Lankā. Then, O king, liberated agreeably to the injunction of the Great-father, the slayer of Samvara and Vritra, worshipped of all the celestials, went (back) to heaven.
In the Lanka war, Indrajit had defeated Ram and Lakshman once and whole army of Ram including Ram and Lakshman with exception of Hanuman and vibhishan on another instance.
Hanuman had defeated Ravana in physical duel nearly killing him in their first encounter. And also severely weakened Kumbhakarna along with Sugreev making it much easier for Ram to take him down. The same Kumbhakarna who couldn't be scratched by the contemporary Devas and asuras even united., the same one who laughed at Indra's Vajra and defeated him, forcing him to flee to Brahma.
Hanuman also revived the whole Vanar army along with Ram and Lakshman who were incapacitated by Indrajit.
Jāmbavān said,—"Hear, O foremost of Rākshasas, why I enquire after the Wind-god's son. While this hero is alive, this force, albeit destroyed, liveth; but if Hanumān is reft of life, although living, we are destroyed. O child, if the Wind-god's offspring, resembling his sire himself or (the deity of) Fire in prowess, is alive, there is hope for our lives".
Both single handedly could change the tide of war. That too which is a scale of quadrillions of times greater than the Mahabharat war and participants were exponentially more powerful.
Neither Bhishma nor drona, even in their prime and fully intended (In the Kuru war, both restrained themselves greatly due to affection to Pandavs) can do anything against Hanuman or Indrajit. They are simply on a whole another level.