I don't think any of the cameras that have been mentioned have the ability to "talk back". Hopefully this isn't a deal-breaker for them.
Maybe they can set up just one such camera or a separate system to achieve this at the front door, for example.
Yea, from the research i've done there is not a great solution for this on these types of cameras. I've been told it's not worth the effort/money to attempt to get these to be able to talk both ways. I'm going to suggest they get a doorbell camera for that feature.