If your son-in-law is a "US person" (you aren't clear on this) for income tax purposes, he must report the gift. No gift tax is owed unless his lifetime gifts and estate is more than $11 million.
Gifts received by a US person are only taxable to the recipient under rare circumstances, such as if your son-in-law gifted you a piece of US investment or business property or certain other physical assets that are within the US. Money is not a physical asset and so gifts of money are never taxable to the recipient.
