plural...

overheard a conversation between s.b. and friend. discussing the plural of the word focus. they said it was foci, but second guessed. is it foci? is that right? so, they began with the known:

octopus, octopi.

fungus, fungi.

jesus, jesi.

jesi. none of us saw that one coming. a brigade of jesi. a flock. a kindness. a murder. a bevy. a brace. a bloat. a parliament. a herd. a kit. what is the correct term? a swarm of jesi? a gaggle? a flight?