There's a huge huge difference between meeting someone and actually living with someone, or being in close proximity with them, and therefore having interactions with them that go beyond things that you're probably asked to say.
Again, you wouldn't ask someone what colour their baby will be because that's too personal and therefore rude. Asking someone you live with or communicate with almost daily (because they're now family) is a whole different thing because the personal boundaries are less clear - stuff such as what colour a child would be is fine to ask if you're curious (which is what I think happened here). The conversations you have become far more personal and of course less scripted.
Do I think the RF is racist? Oh definitely. However, I don't think the fact that racism that may not obviously be racism to them but is to the general population, which actually has to interact with different cultures on more personal levels than diplomatic meetings and respect the developing culture regarding 'political correctness' (the word has harsh connotations but it's the best I have to offer lmao), makes them the most guilty people out there. Unless the comments were repeated after they were explained that the couple didn't feel comfortable with them, then yes you're very quickly slipping into a discussion where racism goes beyond just blissful ignorance.