Currently, if they own or control any foreign bank accounts where the balance is over US$10,000, that must be reported annually, the report is called FBAR, and it can be done online. No tax is owed, hopefully they have been making regular reports.
https://www.irs.gov/businesses/small-businesses-self-employed/report-of-foreign-bank-and-financial-a...
As to the transfer, there are no tax implications when a person transfers money they own from one account to another account, even if the accounts are overseas. If there is interest or capital gains, that is taxable in the usual way. The banks are required to report transfers of more than $10,000, but that is just a reporting requirement and involves no action on the part of the account owner, the bank does it automatically. Note that structuring the transfer to avoid this reporting limit (such as, structuring a $50,000 transfer into 6 transfers of less than $10,000 each) can sometimes constitute a financial crime even if the money is otherwise perfectly legal. So just make whatever transfers are wanted, and don't monkey around.
