Why pay a secret visit to Eug and Jack in 2023 if they had already bought a property when they left Frogmore in June 2020? It sounds a more recent purchase if true, and could be related to the Stoat's US visa difficulties although those seem to have been ironed out for him. Portugal could be a halfway house for them between the US and UK, though as the UK isn't part of the Schengen Area she'd not be able to come and go to England.
I wonder if the Flatpacks could be formalised in Portugal, get visas somehow and become Flatpaques Portugueses?