Moving from Ireland

You would have to apply for residency within 90 days of arrival with a full year's medical insurance paid up front. You will automatically become tax resident after 183 days here but if planning to move in November 2022 you would be liable for Spanish tax from 1/1/2023
Your son would need to go to a private international school such as
https://www.laudeladyelizabeth.com/wp-content/uploads/2021/02/LES-Schedules-of-Fees-2021-2022-1-Revised.pdf 

Unemployment figures for the under 25s in Spain are usually one of the highest in Europe. When old enough they would need to take a driving test in Spanish.

Living here is a whole different thing than holidaying and some areas can change significantly from summer to winter.

https://www.meteoblue.com/en/weather/14-days/calpe_spain_2520496  

Just as a guide, although these temperatures may look a lot better than at home in Ireland, it will feel a lot colder than this indoors and you will need to find something with a good heating system.

https://www.kyero.com/en/moraira-villas-long-let-1l1499g2?f%5B%5D=near_shops&f%5B%5D=garden&min_beds=4

I agree with Cheryl,  she has given excellent advice. You do indeed have to apply for residency within the first 90 days and comply with the income and healthcare requirements. 

Steve 

Above advice is excellent.

You need tax advice ... you may be working/earning remotely, but you will need to be Spanish Tax Residents.

If you have good incomes, you will find the Spanish income tax-take to be high; so get the advice before you take the plunge.

"we are Irish residents and Spain is the EU, I take it we have freedom of movement and don't need to do anything but turn up, organise local health insurance , school etc?"

It's not about residency, do you have  Irish passports?

Yes

This may be of interest to you:

https://www.dfa.ie/irish-embassy/spain/our-services/new-to-spain/residency-and-entry-requirements/#main-content

Steve 

You don't describe your remote working situation. If you will be working remotely but employed by a Spanish company and on a full-time Spanish contract then you will be covered by the Spanish social security and do not need to show any proof of private medical insurance (at least for you...not sure about the rest of your family).

BTW if you are working remotely for a company that is outside of Spain but has a registered office in Spain then you need to be officially re-assigned to the Spanish office and given a Spanish contract. (At least this is how it was a few years back when I was looking into this.)