If they are US citizens they must report all their world wide income on a US tax return and pay the appropriate tax. If they also pay income tax in a foreign country there is a deduction or credit for foreign taxes that should partly or completely offset the US taxes.
The transfer of that much money will automatically be reported to the IRS, whether they transfer it to themselves or you. The transfer itself is not taxable but it may put the IRS on the lookout. Professional help is recommended since the cost of a mistake could be considerable.
