Zaire has many other living relatives. From Nandi’s line alone, there’s Zaire’s brother - Kakinga (born 1978), who sired 13 offspring at the Calgary Zoo (seven currently living) before his death in 2016; and Zaire’s brother - Motoba (born 1983), who sired five offspring (all currently living) and has had 15 grandchildren (10 living) through his two eldest offspring.
I think the best way forward is to form a new breeding troop of 1.3 with the remaining females Effie (1993), Mjukuu (1999) and Alika (2014) being joined by a new male. The two options for introducing a new male are to introduce a young male (who could mature in the troop; and wouldn’t pose a threat to the two juveniles); or wait until Alika and Gernot have reached adolescence, export Gernot and bring in a new male. I don’t know the females well enough to comment on which option would potentially work better.