If you’re oldest is 12, he will make a choice to stand up to his dad at some point soon.
Your ex will do what he will do, you must rid yourself of the notion that your efforts to appease him mean anything.
In fact, he will always escalate his behavior in order to get some reaction as he is addicted to this behavior.
I thought that from 12 years old in the UK, the child could have a say about which parent to live with, and how much contact, if any?
Your ex is escalating his controlling behavior to your oldest. He is scared that he will lose control so he is using everything he can to bind him to himself.
This works to your advantage because your son will want to go through the natural stage of growing independent from his parents as a teen.
Have a discussion with your son. He probably doesn’t realize how much say he has. Tell him he can be strong and decide what he wants for himself, that he doesn’t have to appease either parent.
You don’t have the resources to fight your ex in the court, but for your eldest, it’s irrelevant anyway. By 14 years he can choose for himself. You don’t get any money from your ex and it’s a case of what your DS says, goes. Your DS needs to think about that.
If he decides he wants to leave your ex’s house and come to yours at any point, he can get you to send someone to collect him, or even ask for the police to come and check that he is not being imprisoned against his will when he wants to return to your house. They can make sure that your younger one comes at the same time, in accordance with what was legally agreed.
I think you should try to talk to a few solicitors and investigate getting a loan to get someone to explore how to sue for at least some of the child benefits that your ex has withheld that were due for your older son, as well as for damages for slander, harassment, intentional emotional distress, stalking etc.
You need a legal eagle to assess your situation.
Once you have assessed what you could do, get them to send a cease and desist type letter stating that if your ex doesn’t fully back off, you will pursue every legal avenue.
There is a new domestic violence bill being drafted at the moment and it could be relevant to your situation.
As an aside, it’s a long shot, but have you checked any of your insurance policies to see if they offer any legal advice over the phone? I did this once, it was actually horse insurance and my question was totally unrelated to that, but the person on the end of the phone gave me all kinds of useful information and advice.
Does Citizen’s Advice still exist in the UK?
I know you feel defeated but it’s actually the dread of what the abuser might do that is the hardest.
He doesn’t have to do much at all.
Use your time to think of all the ways you could possibly fight back.
Even if you don’t have the strength right now, you can hold the information in reserve for when you feel stronger.
Just knowing that you have something up your sleeve will help.
In a few short years your two elder DS can start deciding for themselves.
Anything could happen to get your ex off your back. Karma.
Focus on your future, not his. Sorry that your partner is unwell, but at least he got his op before the current situation where everyone is self-isolating at home anyway.
You can do this, you can have a future filled with hope and love.