Why don't you just exchange Bitcoin for cash, and then top up your bank accounts with cash via ATMs? It seems to me that this way banks won't be interested in sources of income.
At least in my country, banks only have questions when funds are deposited to the card from cards of people who often interact with cards of other people. This is why you are under surveillance. Topping up cards at ATMs does not raise any questions.
Currently my country also prohibits the purchase of goods using bitcoins, but we can use the exchange to convert bitcoins and then exchange them for fiat currency.
There is no problem with that because I have been using it for a long time and I think there are no questions from the bank because we are making deposits in our own name.
Even when you deposit directly at the teller, there is no obligation for them to ask the customer and if they do, it is probably just a courtesy as usual.
For the case of filling through an ATM, I think it is much easier and there will never be any questions from the bank.
I suspect the amount was so large and unusual for him to deposit that the bank would be monitoring where the funds came from.