Partner spent my money and lied

This lowlife scum of a "partner" is actively making your life worse. And that of your children. You know he is a liar and a cheat and a gaslighter. He doesn't give a shit about you because he knows you'll take him back and now he's proven that he doesn't give a shit about the kids because he's happy to steal their money. He is a father and he's comfortable enough to gamble away money for his children's future and then lie about it to your face.

I know this is a bit of tough love but you really need to have a think about that, hard. Your children deserve better. Your family can see him for what he is. It is time to step up and do what is best for your children because he isn't going to and at the moment you've let them down. But that can change.

Look up the Freedom programme OP. And keep posting on here for support. I would bet my house that your anxiety would drastically improve if you kicked this guy out and never took him back.

See? You KNOW he is the cause of so much of your mental health problems, rather than a help
If you can manage to get away from him, your health will improve massively and so will everything else in your life. You and your children deserve so much more

You gave a gambler 15k. WHY??

Would you give an alcoholic a barrel of whiskey.

Are you telling your therapist everything that is going on in your life? If they know have they signposted you to a domestic abuse charity or the freedom programme?

This is such a reassuring thing you’ve just said to yourself, OP. You can see how he harms you. That’s very real. He is doing this. You have only to gain by freeing yourself of his horrendous influence.

And he knows what he’s doing. It’s why he caused a stink with some BS “disrespect” line about your sister being named first as executor.

It is so unbelievably remote a risk that her children sue her, that she doesn’t make them whole, that she sues the husband.

It is if at some point in the future her children realise they have been done out of their inheritance and they pursue it like the case linked above.

It is an issue if she tries to sue him to return the money and the court will find out that she has acted in breach of her fiduciary duty.

I am amazed at many people think it is perfectly OK for her to act this way with her children's money when she has been put in position as Trustee. Its no different than if she were a Trustee of money in trust for me or for you and she decides to give it to someone who can't be trusted.

Good news! You can do a will online for super cheap - like £20. Don’t tell him you’ve made it. But tell your siblings.

Totally this

All you need to say to this is:
"You have given me no confidence that I can trust you with mine or my childrens money."

Please get try to get some therapy for your health anxiety and self-confidence while working on trying to get the money back.
It is unlikely you will die while your children are young, don't let this fear keep you with a partner who lies and doesn't care about you.
As others have said, you can protect their inheritances with various will arrangements even if he did need to be sole carer of them for some reason.
Get strong and get away from this dude.

Do you have an illness where you are terminally ill to be speaking like this? Are you expecting to die (realistically) in the next few years?

I dont particularly like the thought of my sister (also in her 20s) looking after my child now, but then again, I am not expecting to die (unless it is a tragic accident etc)

I know you said your mum has cancer and died very young which I think has led to a lot trauma you are carrying.

You now know the symptoms to look for, however. And you are more aware of this disease to be proactive in staying healthy.

I would also seek out some counselling for your mental health - it will do wonders for you

Start speaking to him again and get the £2k immediately. Pressure him and his friend for the £3 back. Don't trust him with money ever again.

Please get rid of this dead beat of a man!! Have some self worth, you’re better than this.

Making them beneficiaries and your sibling/s executors/trustees doesn’t mean your siblings have to take care of your children until they’re 18. It just means 1) your kids get your life insurance money pay out and 2) it’s on your siblings to pass them that money.

And if you have a will, please re do it so the bastard doesn’t get anything, isn’t even mentioned etc. if he’s a trustee or executor for anything, you can bet your ass he’ll rack up costs (that will come out of the estate) for “performing his duties”

I think you might not get that money back unless your prepared to go to court and even than, it could be your word against his. It's a horrible thing what he has done especially as it's for your children but money brings out the worst in people. He's either gambled it, got into some dodgy scheme with his mate or tried to buy some crypto or get rich quick thing. Or spent it on random things.
He will argue with you every time you ask to see the bank account or say you don't care about him and only care about money. It's what people (man or woman or any gender) say when they have something to hide.
Don't play nice, it will be a carrot dangled in front of you. You take the action you can

As he is the children’s father you would think this would be a safe enough thing to do!

Maybe not with his history though.

I can't even fathom the tiny difference there must have been on 4% as opposed to 2% on £15k for a few weeks. Not enough to bother with I wouldn't have thought. I'd have stuffed it in the 2% account and just opened a higher interest one the following day.

I would have thought that no one would be better than him.

If you left him & stayed away I'm sure your family would help.

Make the kids the beneficiaries of the life insurance policy, and specify that your brother and/or sister are the trustees. You can also make them the executors of your estate in your will so your partner isn't in charge of the kids' money.