It absolutely has to be an agreement between the prospective parents, obviously someone is going to have their wishes thwarted. Only they can know how a third child will impact on everything, their time, their finances, the space their house affords, and last but not least the two children they already have, so there isn't really any definitive answer. I don't think the husband's pov is unreasonable he has an eye to the future and probably sees another child as a disruption to what has already been established.
A friend of mine went for a third child, at the time, they had a son and a daughter, close in age, 5 and 6. Her husband was somewhat railroaded into what was primarily the wife's decision at the time. Their daughter who became the middle child was pretty ok with her new brother, but the son who had to share a room before they moved never really bonded with him, a certain amount of resentment and displacement was felt. For the parents having to go back to that interminable and somewhat chaotic baby stage at a time when they had the first two established in a routine at school also caused a certain amount of upheaval at the time. Well of course they wouldn't be without him now that goes without saying.
As everyone else has stated, it's up to them to work it out.