Resembles approach used by me, except I gave them not keys but two SEEDs combined be special way ( known exclusively to me) and divided into several parts using Shamir Secret Sharing Scheme. So even in the case those three groups ( to whom those parts were handed over) somehow spot each other they will not able to access my 2-of-2 multisig wallet.
Mine is just an idea of how I do it. I am pretty sure everyone has their own custom idea. Here the key was combined with Seed + Master key of the 2nd wallet.
I also have another way to store my key:
The wallet has extended seed and few words of the extended seed are in my memory and shared with one person who only knows the missing words but do not know the use of the words.
The seeds (regular and extended) are printed without the words are in my memory and sent to two people who do not have much connection with the one knows only the words but if something happens to me then they will surely meet and will talk about it. And this way the person who knows only few random words will connect that this was a part of the seed.