I'm not saying anything, rather I am posing queries to which I would like answers. Nothing in this post is certain !
I suspect that if a specific bequest of item A is made to benficiary A, then beneficiery B cannot be held to own or control item A, so if it is a PFIC then any problem is avoided.
But if an unspecified share of assets rather than a specific allocation is made, then I don't know at what point the ownership of a PFIC passes under a will. Does entitlement under the will exist at the point of death - does this also imply ownership at that point. Then transfer of the asset months later, or even sale for cash before distribution may not mean that you did not own yout share at some point.during the probate period. So I'm not sure where ADAM stands.
I don't think you get the capital gains step up on a PFIC either.
If the deceased has a UK will, the assets are in the UK, and death is in the UK, has US jurisdiction any part in the probate ? An advisor I would rate as very competent told me that there is no need to have wills in more than one jurisdiction (UK and US) unless there is real estate involved (perhaps specifically US real estate) regardless of where the other assets are. Having only one will certainly simplifies things. This may not apply if the non-US country is not the UK. But there may be circumstances in which this advice would be wrong ?
I suspect that executorship is also a nasty trap since you then gain signatory authority over everything and hence lots of FATCA trouble. But I believe one can refuse or be unable to take up appointment as executor. Does that let you off the hook ?
The biggest problem I face actually, is denial by some relatives that there is a potential problem, and hence obstruction to re-arranging things more advantageously. It is upsetting to discover how suspicious otherwise amicable people can become.
The bottom line is: Find and pay for a top-notch tax lawyer, and having paid for top-notch advice, TAKE IT. If expedient share the advice with executors and beneficiaries so that they know why you are doing this or that. A good advisor will also be on talking terms with relevant jurisdictional officials and be in a much better position to negotiate a sensible resolution of difficulties. How do you find such an advisor ? Well, perhaps through a forum like this or referral by your family solicitor. But go to meet them personally, being informed and knowing what awkward questions to ask at the initial meeting. If they don't display off the top of their heads an immediate grasp of your situation by citing relevant exemption brackets, tax rates, and showing familiarity with fiscal regulations and similar situations they have dealt with, then walk out.
PS. I hope this is not a replica post - I was logged out just before I pressed the SEND button.