Andrew Goodman

You first need to identify whether your husband is UK tax resident for the tax year - search for HMRC RDR3 for guidance. If he is UK resident then he will be liable to UK capital gains tax. The treaty does not protect him due to art 13(7). He may also be liable to tax in the Netherlands, in which case he should get credit for one country's tax against the other under the treaty. The country that has to be paid first will depend on where he has a permanent home or, if both, the "centre of his vital interests" which seems likely to be the UK. If he is tax resident only in the Netherlands, he would not have to pay UK capital gains tax. He may have to pay Dutch tax. However, if he is non-UK resident for five tax years or less, he could be taxed on his return under the "temporary non-resident" rules. Essentially, the treaty is unlikely to protect your husband unless he is non-resident for more than 5 tax years.

For what it is worth, under current law: i) Yes, provided you remain employed in the US until your return to the property (although, to be pedantic, it is a relief rather than an exemption) - see TCGA s.223(3)(b) ii) Yes, provided you remain employed in the US and meet 223(3B)(b), which you probably do, given it would be a long commute otherwise: "in a case falling within paragraph (b), (c) or (d) of that subsection, the individual was prevented from resuming residence in the dwelling-house in consequence of the situation of the individual’s place of work or a condition imposed by the terms of the individual’s employment requiring the individual to reside elsewhere, being a condition reasonably imposed to secure the effective performance by the employee of his duties" If you buy a US home, I think your UK home might still qualify but you would need to make an election within 222(5) within 2 years. definitely don't rely on that any more than you would any stranger on the internet.

You are confusing domicile with residence. They are different things. The relevant test you are looking for is residence. As to whether you are resident in the UK: https://www.gov.uk/government/publications/rdr3-statutory-residence-test-srt/guidance-note-for-statutory-residence-test-srt-rdr3

Not forgetting stamp duty land tax (SDLT). This could be payable despite no money changing hands.