You'd be better off asking this to be moved to the Living Overseas section for better advice. Normally now you need a visa and medical etc to move to the EU. Why would you do it for a year? Especially with primary aged children. The hassle will be immense especially for school etc. As someone who moved abroad, it can take a long time to "settle".

Do you own a property? My English has Spanish residency, but is struggling to know how to move there long term as he owns a at which he will have to pay tax in Spain if he rents it out in the uk (or something along these lines

Posted too soon! I know he's also having an issue with taking his car there and working for his uk firm (he can only work there for 3 months without paying tax in Spain also). Which of course makes sense if he's using their services, but I know it's been a lot more complicated than it was was pre-brexit.

Go on YouTube, lots of vlogs on there with expats & people advising. Portugal actually looks relatively straightforward for an extended visa. No personal experience tho.

How old are the DC?

I have no idea what the rules for Portugal are, but I would suggest searching for relevant groups on Facebook. (This is based on having come across a FB group that is a very useful source of information for applying for a visa in France.) In the case of France it would generally be difficult to get a visa that would allow you to work as an employee. Broadly you would need to find an employer that was willing to apply for permission to employ a non-EU citizen. The employer would need to show that it had advertised the post and been unable to find an EU national to fill it. However, each EU country will have its own immigration rules dealing with immigration of non-EU nationals. I don't know how Portugal's rules compare to those of France.

I looked into relocating to Portugal with young ds a few years back. In the end I decided against it as it was very hard to find long term rentals - they can charge so much more for the same properties in the high season, that many will only let over the winter. I was worried at the potential of being being made homeless or forced to pay extortionate holiday let prices over the high season.

So my recommendation would be to carefully research housing options.

I lived in the UK but moved back to Portugal a few years ago (I'm Portuguese btw). The thing about Portuguese culture is that we're incredibly biased (in a good way) regarding foreigners. There's this allure of excitment about people being from somewhere else and that should help you to settle here.
Legally, you should get a job before moving here BUT in reality it's actually easier. You can come and visit for 3 months (with the regular holiday VISA, you don't have to apply because there's a treaty between both countries). During those 3 months you can then look for a job and then you take that contract to the "SEF" (that's the Portuguese equivalent to the UKBA) and you'll be given a temporary VISA while you wait for the permanent one. If the boss wants you, they won't be bothered about you not having a permanent VISA because it's not difficult to sponsor a worker (although Portugal is all about red tape it's not for this).
It shouldn't be this easy, but it is. I first started noticing a lot of Brazillians working at the mall even before the pandemic and then finally asked the cable guy and he told me "this is how it's done".
The most important is whether you have a skill, that companies want. Depending on what you want to do, not speaking Portuguese won't be a problem.
Registering with a GP isn't an issue from the legal point of view (you don't need a permanent visa) i.e. it's easy but it depends on them having a vacancy and therein lies the problem that'll likely make you despair at times.
Resgistering with a school won't be an issue either.
Renting will be a problem. For the first 3 months you're better off renting an AirBnB. I'm a landlady and if I were to rent for a short-term I'd up the rent so I'd expect others to do the same.
Good luck!

*important thing