Much of your post is beyond etiquette, but to answer your question about the gifts: I would only give her gifts in person.
This woman sounds like a nightmare - https://uk.news.yahoo.com/residents-reveal-parking-war-with-selfish-mum-who-blocks-roads-with-4x4-134437513.html
Hopefully some authority will stop her - short version: She drops her kids at school and parks wherever she wants, frequently blocking peoples laneways for up to 45 minutes.
It would be so tempting to buy a wrecker car, and "ooops, did I just hit your car? Let me move. "Ooopss, wrong gear, sorry to hit you again." Not that I would do it, but one can daydream.
We have some friends who have a teenage son who is a picky eater. We will occasionally visit each others' houses for events, like big games on TV. We had them over a while ago and I made lasagna (normal, no weird veggies or anything) and the son just picked at it and left most of it on his plate.
I would've been much happier if he'd just taken a small piece if he's not sure that he'd like it, so a large piece doesn't go to waste; my kids DO like it and are always willing to warm up leftovers for subsequent meals, so having extras is nice.
Our relationship with these friends is kind of informal. They were supposed to come over today for a big game but ended up not coming so the point is moot for now. But tell me....for future events, when I make a big meal, would it be okay to say to the son, "Hey, take a taste to see if you like it. If you don't, no biggie....here's X and Y that you can eat instead. If you do like it, take as much as you want!"
I would just hate to see something wasted just because it's not to his taste but he feels like he HAS to take a big helping. I wouldn't be offended if decides he doesn't like it and doesn't want it. Is there a way of conveying that without sounding overly micromanaging?
I don't understand why cheese is a mandatory ingredient in fast-food breakfast sandwiches. I don't like cheese with eggs or sausage, but it is hard to find a cheese-free version. Asking to skip the cheese seems to confuse the cooks, and the sandwich ends up with cheese anyhow. On the bright side, I'm never tempted to stop at a fast food place for breakfast.
DRINK lots of WATER.
Be aware of altitude sickness. Give yourself time to adjust
Oh, chapstick will be your friend!
DH has hearing aids and even when he is wearing them, he has a lot of problems hearing in crowd situations.
He has to pay attention to single out 1 voice and if everyone is talking at once, it all becomes background noise. There are times when its easier on everyone if he takes them out and relies on me to translate for him*. He has mentioned that family gatherings are harder on him because family members tend to sound more similar than strangers do.
This could be a part of the reason Aunt doesn't wear her hearing aids around family.
*Not really translate, he just needs to only have to pick out 1 voice instead of trying to hear voices in different directions. Perhaps someone could do that for Aunt?