Thanks!! Yeah, I probably need an expert! Curious if others had dealt with this though. The best case is that we get to write this off, the worst case is that I can ignore it.
Write what off?
Edited: What position does the UK tax authority take regarding value, taxes, etc?
Sorry for my imprecise language, I meant "deduct the loss." He has already dealt with the UK tax authority. It was a small capital gain there, but tax was not due. He has all that documentation. My understanding is that the UK position is not relevant because he is a US resident (unless, e.g., he can take a foreign tax credit, which he can't). We are required to use USD as our functional currency, so on Form 8949 we definitely see a loss: If the house had been sold right when FIL died, we would have gotten $76K, but instead we got $70K. Interestingly, if it had been sold right when the widow died, we would have gotten $80K, but the pound tanked right after that.
I believe, as suggested by Drifterrider, the widow had a "life estate." But as she was never an owner of the house, it's unclear if the value would get stepped up at her death? More importantly, can we even deduct the loss since she had "personal use" of the house? When she died, can we argue that the house was then converted from personal use? Would it be considered "restricted property" before that time and hence it was not "vested" until she died? It was sold about a year later. If we had been able to sell it right after the father died, then my interpretation is that any loss is deductible if the heirs do not use it as a personal residence. I find no clear guidance on our situation though.