I agree with this.
I remember the first thread and I thought the forced family dynamic was odd at the time. This update isn't any less weird.
The OP has been generous to provide the caravan at no cost - but she has pointed this out on many occasions across both threads. It does make me wonder if she's like this in real life? I know someone who's like this, if they do you a favour they like to remind you how benevolent they've been at every opportunity. It has the effect of making people want to avoid them.
Forcing family members to attend a weekly dinner in return for free board doesn't create a close and loving family. It's a simulation.
Asking someone to give up one day of their weekend every week is a big ask. And yes, it's "only" dinner but smack bang in the middle of the day and I'm sure OP would be horrified if he turned up, smashed down the food, and then rushed off, so it does effectively bugger up the entire day. Every week.
OP seems to consider it her role to teach her nephew about the reality of the world because she has referred to "nothing in life being free" and her rules reflecting this. I don't think it's her place to take on the role as moral guardian for her nephew, and nor would I expect close family to treat me a certain way just because there are different expectations out in the wild!
I agree with PP that this just seems to be a battle of wills, nothing more. OP has said that 15 people already attend the meal so it doesn't really matter if nephew attends or not - it's just a pissing content, essentially.
There's no discernible benefit to forcing someone to sit in your company if they would choose to be elsewhere. Even when you're offering free food, they would rather spend their time elsewhere. It's degrading to insist on them still turning up.
It's even more degrading when you consider that OP considers her company to be equal to some kind of chore that her nephew owes her in return for living in her caravan.
I think it's a massive shame that your nephew doesn't want to voluntarily spend any time with you OP, but given your comments here, I wonder if there's a reason for that.
As PP have said, your caravan, your rules. You're entitled to enforce whatever rules you choose, but doesn't mean that they're reasonable, proportionate, or even particularly sensible. But yes, it is absolutely your right.
I hope your nephew manages to find someone to stay for the next year without too much hassle.