I have mixed feelings about your story and doubts about its veracity.

You claim that you didn't take into account this money (2.5 btc), which means that you don't lack finances. Then you are ready to move to another jurisdiction because of these old "crumbs" left in your wallets, just to pay less taxes.

You also claim that you want to do everything according to the law, but at the same time you are looking for a way to evade paying taxes in your country (you are even ready to move to another country). Another contradiction. Do you want to evade compliance with the law within the legal framework?

OP is likely looking for the kind of advice people like Zuckerberg would be looking for.  Millionaires and billionaires are always on the lookout for more ways to avoid taxes.  Unfortunately, most of us who pay the taxes are the poor.  The heaviest is always on our shoulders, never on theirs.