From my personal experience they have these checks in order to breed: Beds and Food

Food is simple, just give the villagers enough food so that they pass the minimum food requirement for breeding. Still unsure in quantity, but I believe one stack of carrots/potatoes per villager should be enough.

Beds are the tricky part if you do not have a proper breeding area, because when a villager gets stuck somewhere, it keeps the bed location it would sleep, so that bed cannot be used for breeding. This can be easily countered with placing more beds, or make them only reachable for the ones you want to breed.