US resident minor grandchild inheriting legacy in UK will

Hi everyone

My father (UK citizen and resident) has left each of his grandchildren (including my two minor children) a GBP5,000 legacy in his will. In UK terms, I think it would just create a bare trust, as the will simply states "to each of my grandchildren alive at my death on reaching 18 the sum of GBP5,000".

I'm a US resident green card holder, and my two children are US resident, dual nationals. The Executor of the will (my sister) is UK resident and a UK citizen.

My aim first and foremost is to set up a trust with minimal legal costs eating into the legacies. Secondly I'd like the flexibility to invest the funds on bahalf of my children, ideally in the US to avoid PFIC complications.

Before I start wading through UK trust law for non-resident trusts (including the UK and US tax implications), and US trust law, has anyone here worked out how to deal with something like this?

Many thanks!
Martin

As there have not been any detailed replies, I shall make some comments that may assist.
The legacy, as it has been described, is contingent on the relevant grandchild reaching the age of 18. That would make the administration of the estate unduly complicated. It might be better to make an outright gift to each grandchild, and then to give powers of investment to a parent while the child is a minor.
There is no reason that the power should not allow for investment in the US.