I have made the password quite challenging, but at the same time it is possible to commit it to memory.
Can you tell me, if I lose or forget my password, how would I retrieve my coins?
That depends on what you consider challenging. A simple passphrase could be bruteforced in seconds or minutes. A complex one would perhaps require millions of years. It's easier to say never in that case.
Because as I understand, I have one seedphrase for the two wallets (hidden, standard).
Would I need to enter the seedphrase in another device (eg. Electrum) to get my coins back? And would they all appear "together"?
If you have 0.1 BTC in your standard wallet and 5 BTC in your hidden wallet, here is how it would work. If you enter your seed in Electrum and choose BIP39 and the correct derivation path in the options, you would recover that 0.1 BTC. To gain access to the 5 BTC, you'll need the correct passphrase on top of that. So those are two different wallets. And the passphrase has to be
exactly the same because there is no such thing as a wrong one in the protocol's eyes. 'Sumarokov' will recover one account, 'sumarokov' a completely different one. The recovery of your coins depends on you entering the identical passphrase. Even empty spaces count as valid characters.
Wow, for the hint with Ian Coleman's's site, but your answer would be more complete if you provided link to this site. I understand that all the necessary instructions are available on this website?
This is the site >
https://iancoleman.io/bip39/.
You should download the latest version from GitHub if you are planning to use it. You can read a bit more here >
https://github.com/iancoleman/bip39.