Slightly confused about Xmas rules please reassure me.

[falleninlovewithScotland]

We've stuck rigidly to the rules on Covid since March so I want to get this right. I've read the Scottish government website 10 times and I'm pretty what we are planning is allowed.
We as in myself, DH DS and his finance (currently living with us) live in in England (level/tier 2 area) and have a second home in Scotland (level/tier 2 area). I have another DC in Scotland in a level/tier 4 area. As soon as lock down in England is lifted we are all going to the Scottish house (as I miss Scotland terribly) will stay till the beginning of January.The DC in Scotland is planning on joining us on the 24th 25th and 26th obviously staying overnight this is allowed isn't it?

The rules over Christmas are a max of 3 households, and in Scotland Queen Nicola has put her own slant on the UK rules to set a max limit of 8 people over the age of 11. www.bbc.com/news/uk-scotland-55085335
So on that front I think you're ok.
BUT depending on where your Scottish house is you are asked not to travel into/out of level 3 and 4 areas except for essential purposes (of which holiday is not one).

House is in level 2 can I travel to level 4 to pick up DS on Xmas eve and take him back on the 27th he doesn't drive? I think I read it that we can, we're fine on the number of people front.

We're travelling from level/tier 2 England to level 2 Scotland so I understand that is allowed I've read the rules repeatedly and that is my interpretation of them. We will travel through a level 3 area but we wont stop off.

Do you have 2 profiles??
At the moment they're in tier 2 / 4, who knows what they'll be in by the end of the month but my understanding was that the level restrictions around household mixing and travel are being lifted for those dates over Christmas.

As I understood it, we switch form all the various tiers to "Christmas rules" 23-27 incl.

So you'll need to look at Nicola's rules to get yourselves into Scotland and then DC needs to look at Nicola's special Christmas rules to get to your second home.

Yes, technically you are not allowed to travel from England (any tier) into Scotland (any level) for any non essential reason before the 23rd December.

www.gov.scot/publications/coronavirus-covid-19-guidance-on-travel-and-transport/#travelbetween

However, as you own a home in Scotland you should be able to justify it - though checking on second homes wasn't allowed in the spring lockdown, as Catherine Calderwood discovered. However this time there is an exception for "travel... for activities in connection with the maintenance, purchase, sale, letting, or rental of residential property that the person owns or is otherwise responsible for." Which sounds like it is you.

It's fine for your family to travel to you from 24th to 26th, wherever they are coming from within the UK.

The rules are only relaxed 23-27 so you should be heading back home on 27th.