They each hold KYC-free sats, with (I believe, at least in USA) a cost basis of the value at the time they received the UTXO.

Depending on the value, this might qualify - for the giver - as taxable gifts (I think the threshold is high, like $15000, but that could be cumulative idk)

It may also qualify as income for the receiver but I don’t know for sure. And our tax law is way behind the reality of 2020s in any case.