Just wait until they have to declare the "gifts" as income when they file their 1040s. They're really going to love Charlie then!
As long as they are considered gifts, the tax will be assessed on Sheen, not the recipients.
There's a $13,000 exclusion each year, but everything after that is an additional tax on the giver. However, there is a "unified gift tax credit" that may be available, if it hasn't already been exhausted. The gift tax credit is basically the amount that could be excluded from estate taxes, and it reduces the estate tax exclusion when you die.
Charlie gave the Bentley recipient a $30,000 check too. That should help pay the taxes.