Advice for a married couple and 11yr old to navigate visa system and best route to take?

Well, there are loads of posts on here already about moving to Spain but it is very difficult for those who want to come for work as a UK citizen. Since Brexit, you would need a guaranteed work placement with a contract that has been verified by the Spanish foreign office. The only jobs that get around this are those in the shortage occupations which are things like medical (though not nursing), high end IT consultancy, medical and scientific research or things like logistic and supply management.

Jobs in the building trade are not a shortage occupation and the unemployment level among that type of work is very high.

If you got a guaranteed job offer, the future employer must certify that the position was offered to EU citizens first and they were unable to fill the vacancy. Pretty impossible, really.

There are other visas such as self employed but you would need to submit a business plan showing the work is in short supply in the area you want to move to, how you could benefit the community by employing local tradesmen and how you would meet the financial requirements to live without being a drain on the social services. You would need to pay into social security so that you are covered by the health services and that payment must be made monthly regardless if you receive an income or not. 

Lots of other visas available from one that doesn't allow you to work to the golden visa where you purchase property in excess of half a million euro or invest a minimum of 1 million euro in Spanish bonds. There is a digital nomad visa where you work for a non Spanish company online and you have to provide evidence you already carry out that type of work and would meet the required income needs.

For a EU citizen, including from Ireland, you can come out and have freedom of employment and a much lower income requirement. As a UK citizen (or any country not in the EU or EEA) it must be applied for in your home country and show a minimum income of 28,800 per year and 7,200 for each family member plus private or state provided (if eligible for an S1) health cover for the whole family.

John123456 on here has made some excellent posts on the type of visas and the pitfalls around them if you read them

Best of luck but meeting the requirements for a non EU citizen is extremely difficult at the moment. 

If you really want to leave the UK and you meet the age requirements it would be very much easier for you to emigrate to Australia,Canada,or New Zealand.Trying to be positive for you.