Oh, I don't know
@Annb. The question of whether to include the 'are' is purely a matter of style, IMO. Neither inclusion or omission in that particular context is ungrammatical.
Whether to use whom or who OTOH is governed by grammatical rules. When it comes to our mother tongue most of us, the world over, grow up copying our parents without thinking about the grammar, but that doesn't mean there isn't any! Learning another language, forces you to remember its rules or you're bound to slip up. In your example whom not who is correct, as you say, because Whom does this belong to? and To whom does this belong? are both accusative case. That was drummed into us at school. (If that doesn't happen now, then standards must have slipped). 'Who' in that context is just plain wrong in my view. I've heard it in speech btw, but not seen the error in print as yet.
I've learnt some grammatical rules in English in school, but English was only taught after I was 13, and at my school the focus was on being able to communicate in everyday life, not proper grammar. Which I think makes a lot of sense, as a starter in a new language you'll want to be able to buy rolls or beer, or ask for the way to the museum, no matter if your irregular verbs are correct (and I've never got - see, I've learnt! - to the stage of anyone explaining the 'whom', although I'd love to understand).
I've learnt from talking to fellow buskers in Amserdam when I was young, and from reading books because translations often aren't as good as the original.
And then I became an active member and a moderator on this forum, which improved my English a lot more. Except for one part: 'bad language'. Because the forum is very strict on bad words, my grasp of your language lacks a natural feeling on cursing, it simply hasn't grown with the rest of my comfortability with it, which is very funny!
I would love to have some more theoretical knowledge. Like you said, when using a second language, knowing the rules can make up some of not having grown up with it.
Slightly more on topic:
I'll have my family weekend, and it promises to be very challenging. Very early start because it's an almost 4 hour drive to where we'll have lunch. Unknown lunch, wing the insulin dose.
Followed by a parcour thing in the trees, right after I most likely completely misguessed my lunch dose here:
https://kanoa.nl/klimbos-zeeland/. I've called them, and there is no way to get down once you've started a route so there's both my fear of heights and a real possibility of a hypo up in the trees...
After that, some of my family members have expressed wanting to go for a cold outside swim with me.
And then there's a meal at the hotel.
So this is bound to be a diabetic
disaster adventure, but I'm very much looking forward to it!
The looking forward taking precedence over anxiety is very much a new thing for me.
I'll keep you updated, but I can't promise my adventures are fitting in the low carb forum...