I am so happy the OP seems to switched on. So much bad advice.
'You can legally keep the house til ds is 18' - no you cant, it's not a legal right and probably wont happen
'She is trespassing' - no she isnt, he is the legal owner and invited her to be there.
'Get a mate to watch ds and ring th door bell ever few hours' - yeah spend you time back and forth, to annoy them. Miss spending time with ds or lose time to spend on the new home. And then when they have a camera put on their door step, get done for harassment. Excellent advice.
'The council house will reduce your settlement' - no it wont. Yes she is housed, but, living in a council house now doesnt mean that she will always keep it or not want to buy a house of her own. A judge isn't going to decide she deserves less and must live in a council house forever if she is legally entitled to more. She may want to.
I know several women who did what the OP did and still got a fair settlement.
OP, it is nice to imagine the shit you would do to them. But you are right to focus and whats best for you and your son.
Get angry is great advice if you can focus the anger in a positive way. Pursuing your settlement, many women dont get angry and dont want to get all they are entitled too. Sometimes because they are so hurt. They need to get angry and realise they are entitled to a fair settlement.
But getting angry and trying to cause all the shit, people here are suggesting will play straight into their hands. They will tell people how unhinged you are, psycho ex, get the police involved if they can. They will bond as though its them against the world.
And if this all back fires on you, you will feel even worse.
They are shits. Both of them are shits. Leave them to willow in their own shit together. I am almost certain their relationship will fuck itself up, because they are both shits. But in the long run, you will be happier.