I guess multisig is making the robbery obsolete, I can have one key stollen, but probably not two at the same time... Multiple backups increase the chances of robbery, if not encrypted. And yes, encryption make me scared of myself forgetting how to access to it 
The best thing that makes robbery obsolete is strong encryption. After a certain length has been reached (and difficulty) they would not be able to acquire your funds even if they could use all of the computing power on Earth in an attempt to crack it. With "forgetting how to access it" you mean forgetting your passphrase, or? I can't really think of good advice for 'backing up a passphrase'. Maybe you could split it into two pieces (2x2 backups) and store them somewhere as well.As said before, being digital nomad, I dont have fix house... I could get a safe somewhere I guess, but if I can avoid to pay for that, or ask banks to keep my btcs, better.
I doubt that there's a free safebox that is actually 'safe'. I recommend paying for these services.Yes I can have 2 trustable people. But... What's about one key on a ledger wallet (with me), one on copay for example, and one in my emails?
Wouldn't you still need to memorize multiple passwords to use all of those?That way I can keep access to my BTCs from anywhere in the world, and I'm guessing they are safe from a hardware failure or robbery. Am I wrong?
Nothing is technically safe from hardware failure IMO, there are life expectancies and device failure rates that variate depending on device type and product. This is why it is recommended to have a minimum of two backups.