When a U.S. person is a beneficiary of an Australian estate what are the risks?

The Ballantyne Family have an established business in Melbourne, Australia and a family office from which they execute on investments within Australia and Asia.  All business and investment matters have always run by the patriarch of the family.

The eldest child moved from Australia to the U.S. 10 years and has married a U.S. citizen and has two U.S. citizen children of her own.

As part of the estate and succession plan for the family control of the family assets will pass to the two children on the death of their father through succession provisions under the terms of a family discretionary trust that own the family office and the business, and any other assets will be passed to two testamentary trusts established under the patriarchs will for the benefit of the children.

Prior to the death of Mr Ballantune the trust deeds and the will was reviewed to ensure thst the trusts do not become grantor trusts under 678 of the internal revenue Code of 1986, on his death.