In laws!!

Next time tell her that maybe if she was a bit nicer to people she wouldn't be living at home at the age of 44!

This is the best option, well done OP! You can also just not participate in the visits to PILs surely, or insist they come to you or meet outside the house. Hope that your DH clearly supports you!

Well done. Try not to think if her either to give you peace of mind.

Practise mental Tai Chi. When she pops into your head, roll it into a ball and gently push it to the side, and replace it with something positive or productive.

Other posters have already said this, but it’s pretty plain she’s insecure and jealous of you and your life. But that’s an explanation and not an excuse for her crap behaviour.
shame as if she was decent and behaved pleasantly to you, guess you’d see her more often.

Not sure why that's defaulted to three 1's!

You tell your husband he has three choices

1. You don't see your sister in law again and will do your best to avoid the kids seeing her as well, it's not good for them to see their mum being spoken to or about like that

1. He speaks to her before you see her again and tells her if he ever speaks to you like that again she will not see you or the kids again.

1. You will stop biting your tongue and give as good as you get, telling her exactly what you think of her next time, which is likely to end up in a huge family row.

I would have replied, "It is a genuine shame that you haven't met someone to have a marriage and family with but it is not my fault. There is no need to be spiteful."

I wonder what she would have said to that.

With all of your updates you really do have to ignore and pity her at the end of the day.

She has such a narrow life still living at home with her parents at the age of 44.
She also has a spiteful and unattractive personality that’s very off putting to say the least.

You on the other hand have a far more fulfilling life which makes for more happiness than she has, or is likely to ever have considering her personality.

Her barbs and poisonous nature are to be pitied.

She is like this because her life hasn’t moved on from her childhood. She is still the little girl of the family living under her parents roof.
She has no concept of having her own family so therefore no understanding. She sounds very immature.

As I said before, pity her.

Just curtly tell her, that you know her brother better than she does actually, its you he shares his hopes and dreams with, shares his children with and life.

He chose to be with you and you are the mother of his children. You are your own family. I would keep referring to your own family to her until she gets it.

Invite PILS to your house or out to lunch somewhere. Make it at a time SIL can’t come or be clear she isn’t invited.

Oh no, make it at a time when the SIL is able to come but don't invite her!

If she's always a dick you shouldn't have been gobsmacked. It's just her standard behaviour.
I'd struggle to be attracted to a man who happily allows his relatives to act like cunts to me.

I think I’d say to her, “I know your brother in ways you can’t possibly imagine,” with a filthy laugh.

Life is too short to waste it with twats, tbh.

I have never ever done the wifework thing, and i certainly never arranged birthday cards etc for my in laws. And my DH had never bothered much before we married. But as soon as we married? MIL and some of the SIL (i had 6) were all "well you forgot uncle jack's birthday, and mother's day" etc etc

I just used to say "i don't have an uncle jack, and i had a great day with my mum" etc, until one day i just told them to STFU and speak to DH. They never did because they just wanted to whine about me and he never put up with it.

well either you say "get to fuck you absolute Bitch" or you stop going to places where she will be.

And either your PILs and DH will be on board with that or they won't. Either of those options.

It is basically (I used the C word) what i said to one of my SILs about 35 years ago and i haven't seen her since. My DH carried on seeing her for a bit but less and less and I'd guess it's about 30 years since he had contact. She is a cow and the other sisters moan about her. And i give them the same advice. They don't take it.

In seriousness though, I'd be telling your husnand very directly that unless he can put a stop to this attitude, the bitcjy comments, and the undermining you with your own children, I'll end up snapping and will NOT be taking any blame in the fall out from that. Much better and nicer coming from her precious brother.

"Oh Jenny, maybe if you find a husband of your own one day you'll understand haha"

"Oh is that so Jenny? Do you think your auntie Susan is more important in your dad's life than your mum then?! Bit weird. Maybe you will understand if anyone ever wants to marry you! "

What a gift, you no longer have to give a shiny shit about her. Your MIL and FIL will have to put up with consequences of her behaviour which are behaving like a dick equals no visits/no interest I her and her sad little life. I'd be clear they are welcome to visit you but SIL is in the bin and not welcome and will not be given any air time. No visits from DCs for her either, I wouldn't expose them to her awfulness