Will poor relationship with SIL evaporate as PIL get older?

You are in control of your life.
You make choices of who you want contact with.
Mute the person on your phone.
Minimise contact.
Minimise thinking about them.
Don't give them the power to take over your mental energy.
You get to a point in life, where you don't give a damn about upsetting people who upset you.
Minimise all contact.
If your husband wants to talk to her and family then tell him to not talk about it near you.

I honestly think you are overthinking it and giving her and the family dynamic too much headspace. I know it's hard not to.

The only thing I'd say is... when your inlaws aren't around anymore, your SIL will have lost whatever power she had. I have no parents or ILs anymore and that means we are all on an equal footing and your SIL will be too, whether she likes it or not.

Last time I saw my MIL she bought a massive box of chocolates for my adult DC to share, and told me they weren’t for me. That’s just fcking rude.*

so what do your DCs say?
Just tell SIL to fuck off if she talks to you, you don't have to care what she thinks of that or anything you say or do. Tell your DH that you are not interested in hearing anything about SIL or anything she says about you or anything even remotely related to her. If he starty, hand up and "no, i don't care"

Your DH needs to manage his own relationships with his sister and parents, you have nothing to do with that unless it starts affecting you and your life. So i the case of the activity you mentioned? "haha, no remember last time? we are going on X date" and that is it. No faffing about pandering to her.

However. This will all depend on how your DC think of SIL etc.

So MIL is a cow too. Honestly, make your life busy with good things and stop subjecting yourself to these people.

You are whipping this up and thoroughly enjoying it. Who cares this much about people they don't live with? Your in laws aren't very nice so leave them to it, even people with kind in laws mostly live their own lives on their own terms. You're obsessed with this woman and it's completely disproportionate to her actual relevance in your life. Do whatever you like, it's nobody else's beeswax.

She sounds awful OP but I suspect that Queen Bee dynamic has been evident before you came along. As she has no children either, it's got worse as she gets older. Her 'family' is still your PIL and your DH, whereas yours is you, DH and DC.
The way I treat people like your PIL who are seeing me as second class until they get a better offer is to say ' you're welcome to join us for Christmas, let us know by x date if you are coming'. I refuse to wait for people to make decisions or change dates and venues ' we're going to x on this date, we've booked for 4 people, let me know if you can join us and I'll see if I can add you'. Don't be pulled into a dynamic where SIL makes the decisions for everyone. Just go ahead and make arrangements and let them do the legwork if they want to join you.

I agree that you can't get rid of this from your life and also have them think well of you.

I know what you mean about any attempt to see one section of the family being accepted but only if you include the others, and then not being able to finalise arrangements. It's frustrating and exhausting.

It's only now that the arguments have become terminal that we've been liberated from frequent huge family gatherings that in hindsight were without exception pretty painful. I feel bad for FIL, who still seems to consider that if we're not all in the same room on a regular basis with photographic evidence of gritted teeth said gathering, that his entire life is a failure. But I'm afraid it's worth it for me not to be subjected to them ever again. (Vivid memories of repeated lengthy discussions of supermarket preferences, which was the only topic we could all contribute to and not argue about). In our case it was only a death that finally broke things. I think it's OK to just stop.

In your case I'd book couples therapy with your dh, and encourage him to go solo as well. For gatherings, I'd start with the date, as that's the bit your SIL is exercising control over - just make the arrangement with your PIL. And tbh i would start doing things you want to do, with people you like, and just tack your PILs on as a side issue, if theyre always likely to cancel anyway. Then you can just say 'Oh well, sorry to miss you, we'll send you a picture from the restaurant/beach/BBQ' and not be inconvenienced.

@NoddyNameChanger But PP also said it's different in her own family. You're not going to change family dynamics in your in-laws that have been ingrained for decades, so you can either let it bother you, or you can grit your teeth and get on with it.

If my MIL had said that to me about the chocolates I'd have made some quip like 'alright Miss Trunchbull' and rolled my eyes. You can buy your own chocolates, she has no power over you.

Your tribe? Honestly you sound like you relish all this carry on. Just stop telling them your plans fgs.

Wow. Bang on.

The whole thread of OP and your response hits home. I am younger than OP but it's all very familiar. I will never be "an important person " to consider even though "son in laws" to PIL's daughters will always be more important than me.

Mine have had the audacity to threaten me to call social services on me when I was a new mom. It was disturbing. I was on a dependent visa and they kept asking me for my "intentions" to marry my DH.

As PP have said lots of time DH is a problem and I agree in my case too. I'm being told that I need to "hug it out" and I refuse to even acknowledge her presence.

Exactly
My DH family are very much of the mindset that if you invite 1 of them they are all welcome but I am not and he agrees with me (even though hes's not quite as brave as me in saying it).
I have got to the stage where I no longer give a shit what they think and I go about my life without them impacting me at all beyond the odd eye roll. Your SIL is taking up too much of your headspace

Quite. You’re pandering to her by allowing her to interfere, faff re dates etc. Stick her on an information diet, just don’t tell her. If pil bang on about her coming, you say ‘No, this is just for you and us’.

You have a busy household by the sounds of it, crack on with your own arrangements for Christmas, ignore her and if pil attend great, if not, there’s only 2 of them, don’t let that get in the way of arrangements. You’re giving her far too much headspace/information. Ignore her shenanigans. Anything you do without pil, you tell nobody, you just get on with it. If your dh is upset, it’s sad, but you don’t need to get involved.

I’m bottom of the ladder with my in-laws and I’m fine with that. I’m top of the ladder in my own immediate family and that’s what counts, but you keep talking about hierarchy - it’s kind of inevitable that you won’t trump your DH’s Mum or sister within THEIR immediate family will you? They were a unit before you came on the scene. Let it go, when the in-laws die you won’t have to deal with her. You seem to hate her a lot more than she hates you. With my in-laws I’m just non-plussed and go along with their plans. With my family it’s different. You just need to grin and bear it with her until the parents pass on.

But why do you care? She sounds spoilt, but once again, that's PIL's fault. Why are you inviting people over when you don't like them and they belittle you? If DH and the kids want to see them, they can go there and you can stay home. Just pull back and stop giving them the opportunity to make you feel bad. Alternatively, invite them all over every few months, have a rubbish afternoon, and know that's it done for a while. I do this with my own family!

If you book a family activity for you, DH and kids and they ask why they weren't invited - oh we fancied doing something just the four of us. Important to get that time. And repeat.

Why is this so hard? You're 50 years old.

People can only do what you allow them to. 🤷‍♀️

And who will the DH actually expected to do the caring? probably OP

Stop being involved. Let DH be the only one speaking to her, tell DH she is not your concern. It’s on him if he gets upset by her. He can be the one caring for his own parents if that’s what he’s up for. Just step back and disengage. You sound like you are feeding off the drama which creates a whirlpool of drama.

Why do you even care? Let the SIL be the dictator in her little hierarchy, don't get involved, if the In laws dont like you then fk them off and dont have any interaction with them, it's DH family, let them deal with it. Your family is your little group, you set the boundaries of what is acceptable within your family unit, don't be dictated to by a SIL, just sod her off.

One challenge I can see is that you and DH will likely get lumped with caring for PIL. That's going to be tough. A woman like her will do fuck all and your DH won't have the heart to abandon them, in spite of how shitty they treat him.

You have a DH problem. And don't bank on the problem disappearing when PIL die. Your DH will likely still play to SIL's tune to an extent as she'll be the only family left and probably alone too.

Well presumably your DH will still be alive and as he is the problem then it won't get a lot better.
She only has any power over you now because your H allows it

SIL has no DC, and her latest LTR is in trouble, that’s why she’s so invested in PIL and what my family are doing.

I’ve 5 adults in my house. Pretty soon it might be double this with spouses and DGC. I just don’t see how what we do, has fuck all to do with her

This seems quite unpleasant. It sounds like you look down on SIL, like you're more successful/happy than her. It actually sounds like your PILs are the problem, it's incredibly rude to cancel because you get a better offer, so call them on that. DH is a big boy now and needs to stand up for himself and his family.

Keep calling it out and laughing it off. Say out loud “sil is determined to be in charge isn’t she?!” “It’s funny how she thinks she’s in charge of my family for some reason!” Etc.

To sil said this or will think that - “Well, that’s a shame, but we’re doing what we’re doing.”

You sound strong willed, just keep doing what you’re doing.

The dynamics really do change once the oldest pass, yes. Sometimes it really is them holding the family together and everyone sighs with relief that they don’t have to do it anymore. But don’t wait around for that. DP could toughen up and help change the dynamic’s by refusing to engage in bs. It just takes a change of mindset.

I would imagine once your in laws are no longer with you, you just won’t see her. She can invite you to her house (to which you have the choice to carpet or decline) or you can choose to invite her to yours if you want to. She won’t have any power over you.