Keep in mind, "pairing" cichlids aren't "mate for life" type creatures.
They mate by instinct, not emotion. The males instinct says to make as many babies as possible. The females instinct says to mate with the "fittest" male possible.
Keep in mind, any number of details could alter situations...
Generally with pairing Cichlids... If one male and one female are together, they'll pair/mate. Although if the female can bully the male she may reject him. Or she may spawn with him then treat him as an enemy while protecting her brood.
If there is an established pair and a stronger male is introduced. The pair will usually defend their current eggs/brood as a pair. But once those offspring are gone, the female will seek the attention of the stronger male. Or will stay back and allow the males to establish who is stronger, then pair off with the winner.
If there is an established pair and another female is introduced. The pair will usually defend their current eggs/brood as a pair. But once those offspring are gone, the male will seek to pair off with whichever female is ready to spawn. Of will wait for whoever is ready next, then pair off with her.
If you are considering exploring a trio with typically pairing fish... Do keep in mind, when two of the fish pair off, the odd fish will be treated as an enemy while they are caring for eggs/offspring. And if the pair are able to kill the odd female, which they most likely will be able to easily do, they often will. Doing this safely would require a very large tank that allows the breeding pair to have a sizable territory and the odd female to be in a different territory with breaks in sight from the pair.
It would be much safer to give each female her own tank and bounce the male around to whoever is ready to spawn. That said, I'd also suggest the male having his own tank for when the females are with a brood or recovering from spawning or sparing. This can very quickly stop feeling like having a couple of fish and turn into work.