I suggest that they look for someone that they can trust who lives outside Nigeria with a Foreign account that accepts cryptocurrency transactions and connects them with their fiat local account. I know it's hard to do but there is probably nothing wrong with trying unless the punishment is imprisonment.
I think they can also open a foreign account if the issue of closure is only about naira account with the banks. They can as well open a dollar account with binance and link it with the bank then transaction can just change to dollar instead of naira and they withdrew dollar instead of the local currency.