Unrelated adults have been introduced in the past in the US with success, so it's quite possible Monarto will be able to achieve a re-introduction between the two brothers. I do think that would be their best bet, as Bahati doesn't have much value breeding wise.
Monarto previously undertook a successful integration of African lion Inkosi (2007) to his half-brother and cousin Jelani (2013) and Mlinzi (2013), so it is indeed possible.
Otherwise, the alternative would be for Bahati to be castrated, which limits options (especially with regards to introducing a new male down the track). There’s no facilities in the region currently in need of a single male.