I think you have to discuss it with your wife? It's her information too. I wouldn't just tell others, because it makes you feel better to, especially if it's "your" friend and not a joint, family friend. There's a certain amount of "need to know" that enters into it too. Is this friend local and a source of help if you need extra people to babysit or check in on you/your wife?

Everyone we know, a "greeting" almost is asking how families/wives/children are. It's not really meant as a serious question and answering "fine" is what is expected. When we tell other people our troubles, it actually can burden them with it! While we may benefit from the relief, we may also have caused them concern, or even anxiety, if they're not able to help us in some way.

I would make up an "inbetween" answer, if you feel you are "lying" by answering "fine" when things aren't fine; I'd just say something like you all are experiencing some health issues but expect things will be getting better. If the other person is nosy or concerned and asks "what health issues" then you can go into a little more detail if you feel like it or not, as determined by your sense of the relationship between you and that person.