If they remain US citizens, they will have to pay US capital gains tax on the sale of their home in the place they now live. They'd also be liable for US federal income tax. This would be on top of whatever taxes they're liable for in the country they moved to.
If they have renounced their citizenship and are no longer resident in the US, then they're (broadly) no longer liable for US taxes, including US capital gains on the sale of their home.
Renouncing citizenship is expensive, but massively cheaper than the taxes they'd pay as non-resident US citizens. I'd assume their income had come in under the threshold or something, so the matter only came up when they wanted to sell their home.
If they remain US citizens, they will have to pay US capital gains tax on the sale of their home in the place they now live. They'd also be liable for US federal income tax. This would be on top of whatever taxes they're liable for in the country they moved to.
If they have renounced their citizenship and are no longer resident in the US, then they're (broadly) no longer liable for US taxes, including US capital gains on the sale of their home.
Renouncing citizenship is expensive, but massively cheaper than the taxes they'd pay as non-resident US citizens. I'd assume their income had come in under the threshold or something, so the matter only came up when they wanted to sell their home.
And somewhere, the world's smallest gold plated violin shittily plays an off-tune medly of mediocrity.