Let's say you live in Spain and your mother in law live in Thailand, if you access her account when you're in Spain, the exchange will detect there's a suspicious activity since a Thailand account get accessed by Spain IP address.
She is from South America and I live in Europe with her daughter. She is with us about 4 months per year.
They will indeed notice that the IP is not in her country of residence. But quite a few people have multiple residencies.
The exchange may also notice that the device (MacBook) that her account gets logged in on, is the same device that a different user (me) uses. But I don't think that's illegal. We are family. I don't know if it is illegal for a family member or friend to manage the account of someone who is old.
She is coming for 3 months this summer. If we log in on the account regularly in those 3 months from the same IP, I don't see the problem.
I can deposit my tokens on her account and whitelist the addresses so there is nothing strange when we cash out.
But maybe I am missing something. I don't know the exact terms and conditions of Binance and Bybit.
I also don't know if they can require KYC (face recognition) again when there is a cashout. Because it is likely that she is in South America when we cash out. That would mean trouble.
In the end, it's all depends on the regulation in your country. But, I would suggest you to do tax avoidance (where you report all of your income and use any way to reduce the tax) instead of tax evasion (where you either report some or not at all in order to avoid paying tax).
I am soon going to consult a tax lawyer to reduce tax legally. I'm pretty sure he does not like the idea above. For example what happens when my mother in law passes away and KYC is required for cashout. Or even worse, me and her daughter separate and she wants to claim ownership of my crypto assets. But this is something I do not consider realistic.
There could be other solutions that I am not aware of right now.
I can use third party apps to exchange crypto for other crypto (stablecoins). But these can lose the peg and I really don't like that risk.
On the other hand I also really don't like to cash out for fiat currency, as this alerts the tax man and he will find me.
There is no way I am going to pay 50% or more tax on profits. This is like voluntarily putting my head in a guillotine.