Honestly, I think table manners would depend on the royal family, their culture, and the period they're meant to represent. Historically, not every king or queen necessarily had the formal table manners we might associate with royalty today. Charlemagne, for example, was reportedly not particularly concerned with refined table etiquette and was even said to talk while chewing and famously burp at dinner.
I also find the idea that a noble or monarch wouldn't cook for themselves or their family a bit ridiculous. Not every royal family needs a butler, either. What if you want to portray a royal family that is deliberately more down-to-earth and closer to the common people than the nobility? A monarch cooking a meal for their family could be perfectly fitting for that kind of household.
For example, why would my Mt. Komorebi royal family, which is clearly based on Northern Japan, eat with a fork and knife simply because they're royalty? If I'm creating a Japanese-inspired royal household, I'd want their dining customs to reflect that culture rather than automatically imposing European aristocratic traditions on them.
I'd rather see different dining styles as optional choices that players can use to define their households, rather than making one particular version of “noble” dining mandatory.