i'm not totally sure elves need to be married to have kids. attempting to find this out, same with humans. if i can manage to get caravan guards for both races trapped in gcs webbed cage traps right outside the depot. not the easiest thing to manage, those things don't like to shoot their loads when they're needed...
i use the legends of forlorn realms mod, which includes several new races, two traders, three antagonists. the other two traders are also targets to cage guards from and try to breed 'em. i've already got breeding females of the other races, including goblins sitting in different pits. the goblins have already had several babies from ambusher and thief visits. and said babies are friendly. the bog trolls recently gave one birth, and i'm expecting one from a voidwalker soon. sadly, though i've got captured kobolds and lizardmen in pits with nests, they won't use them, even with males of their species about. guess they need to be civ members or actual pets to use the nest boxes, sadly. kinda wanted a kobold farm...
and, if you want elves that won't go insane/berzerk/melancholy, you've either gotta get them to attack you and catch some of those ambush/seigers or mod elves so they have caravan guards (which i'd done). seems combatants don't go crazy like the traders do, so you can catch those and pit 'em and let 'em rot while popping out lots of little ones...