I would feel a little upset tbh if this was my husband. They are coworkers and only need to talk about work related conversations. I understand a couple of “how are you?”, but your husband now needs to set boundaries.

Examples he could do it subtly is mentioning you with every personal comment. “I wish you could show me how to swing a bat” respond with “yeah, my wife and I like to go batting every Sunday” or even “yes, my father in-law really got me into baseball”. He should also not ask questions back. If it’s not about work, I don’t think he should really be talking to her on a personal level. At the end of the day, they are coworkers not friends and should really only talk about work things.