2 questions:
- i keep the majority of my BTC on my trezor wallet. do i need to do anything in case BTC forks?

-No your coins will exist pre-and post fork its only new coins created after Bitcoin Core or XT separate that would be affected

- additionally, my my parents bought some BTC because i am told them too invest a little bit and they keep it in a armory wallet. do they need to do anything?

No as well their coins still exist pre and post fork

last question: some people in other threads mentioned that one could double their BTC if they switch to XT. is that correct? and if yes, is this doubling only for the people that switch at the beginning and people that don't switch immediately loose out on this opportunity? or will the amount of BTC double when the majority decide to fork? if i/we need to do something, how can someone using trezor and/or armory make this happend?

If some exchanges accept QT coins while others take XT coins
Your coins would be valid on both blockchains since they are before the forking occured and would trade with value until consensus is reached and one chain is abandoned.

the good part:

that is the reason why are have bitcoin at 250 USD and not 25.000 USD  

Doubt he was.  but if you have a virus you're screwed anyway.
Real cold storage = computer never online.  Don't know if people
are ignorant of that, keep forgetting that, can't seem to bother,
or "think it will never happen to them".  Cold storage, people.
COLD STORAGE!

then that pretty much is full circle and defeats the whole purpose of alt to fiat currencies.

the upside to cryptos is they put you in control of your money.

the downside to cryptos is they put you in control of your money 

simple rule don't put anyone else in control of you cryptos otherwise ur better off sticking to fiat.

I think you unintentionally made my point. For one, your caveat "average Joe who's familiar with Computers and Internet" is not an average Joe. Sure a lot of people can probably logon, check their email, Facebook, etc., but I would not consider them computer savvy. They have a hard time adding a printer or setting up a backup to an automated external drive. Why do you think the plug and play or zero touch configuration market is so huge, most people just want to download an app or program, plug in a device, or use a website and be done.

How are they to know Brainwallet is any less secure than Electrum without putting some time and effort into it? In most cases it would be more than simply visiting a few websites as their technical competence is not as high as almost anyone posting here and they would have a hard time understanding what makes one more secure over the other.

The average Joe I referenced puts his fiat in the bank, if bank gets robbed or if his CC gets compromised, he is still ok with minimal (maybe $50) or no liability. This same Joe maybe hears about Bitcoin, does a bit of research and all he sees is hacked wallets, hacked exchanges, scams, Mt Gox was a scam, etc. on and on. This is what is keeping Bitcoin from exploding. You are not getting 10's of millions of users until much more progress is made in this avenue. it is not simply making something more secure, it is making it more secure and something your grandma, barber, bartender, car mechanic, waitress, little league coach, and so on can use. I think hardware wallets are a step in the right direction but much more needs to be done on all fronts.

they could be scraping or using weak rng...and maybe some fancy elliptic curve calculation where they can determine your curve points once the transaction is made.

i think serious cold storage efforts should involve rolling physical dice.

I'm an average person. I've been using Bitcoin for over 4 years now. I've never lost a single coin.

All it takes is some responsibility. I learned enough (common sense really) to realize that private keys were the "key" to security. After that, it's child's play.

Create secure private keys offline, keep them offline, and your bitcoins will be quite secure.

Learn a little bit about shamir's secret sharing and you will have an asset that is more secure than any traditional asset known to man.

Data is easy to copy, so do it!

There is reliable, open source software which will accomplish all your bitcoin security needs without any additional education (beyond the basics I just mentioned) for the user.

So... I'll rephrase your post as follows: It is far too unsafe to store any real wealth in for the irresponsible, ignorant, unmotivated person. As it should be.

Wrong, the Nasdaq needs Bitcoin to succeed. Nasdaq tranactions will all be run over the blockchain or over a sidechain in the next decade. All other options are objectively stupid and deprecated by Bitcoin's superior technology. All banks are old versions of what Bitcoin can do. Theres no turning back.

As it becomes more mainstream, I think more businesses will get involved to make the payment process easier, to the point where it's just an NFC tap, similar to paypass on a credit card.

The issue he's talking about is that it gets harder to change a protocol when it starts to become embedded.
It's not that the protocol changes can't be released as an upgrade, it's more that there are many devices that will never get upgraded for various reasons. Think about stuff like home routers, for example, that never get an upgrade.
If the network stops completely, people would either learn how to do it, pay someone to do it, or buy another router

Bitcoin involves their money, so I'd think the incentive is there to get the upgrade particularly if they can no longer access their money. Upgrades that just add features will likely not get done.

There's no "too expensive" term.
People will buy what they can.
Much, much probably, 21 millionth Bitcoin adopter won't be able to buy an entire Bitcoin anyway.