AIBU to refuse care for my late dad’s wife?

OP's step-mum was an active participant in OP's father's transgressions. He wouldn't have been able to have an affair and leave OP's mum and his children if her step-mother hadn't been a willing participant in the affair and his decision to leave his wife and kids.

She isn't a blameless victim and OP has no obligation to provide hands-on care for her. OP's sister is unreasonable to expect this.

You refer to OP and her siblings being in their step-mother's home frequently as though the step-mum was doing them a big favour. It was just a consequence of their dad moving out and starting a new family, not a selfless act of kindness on her step-mother's part.

I would stick to your guns.
Tell her no.
The sister sounds like a pita. She needs to arrange carers.

We can't know that, as OP hasn't said. It COULD be that he's tenants in common with the wife and has left half the house to the children of the first marriage, or he's leaving them cash or whatever. OP doesn't seem to care about inheritance, which is admirable.

I wipe my mums. She wiped mine

I'm assuming since your Dad has passed away you haven’t seen your step mum? If you haven’t then it is totally random that after 2 years of not seeing your step mum/half sibling they would expect you to rock up now and provide some level of care.
I have a step mum, no affair involved as my parents were long divorced. My children call her Nanny and she spends time with them, not to the same extent as her own Grandchildren and not as much as they see their maternal Grandmother.
Its likely that she will outlive my Dad as he is older but even in our closer set up I wouldn’t get involved in caring for her when she’s needs that level of input, that will be down to her own children to implement.
Id pop by for a visit, perhaps do her shopping if she needed something but certainly no personal care.
Given your history and level of contact with your half sibling I think it’s very odd that you’re getting messages from others to say your Dad would be disappointed, surely he wouldn’t expect you to have much contact after he was gone?

No, YANBU. You shouldn't feel obligated to help, and given you've never been close to your step-mum, I don't know why she had any expectation of receiving care from you. It was really rude of your half-sister to go around badmouthing you to family. That would put me right off any thought of helping out.

I might offer to help but I’d offer to help any older person. And I might also be more inclined to help a neighbour who’s been good to me.

But I would t apply a tit for tat logic to my SM. The Op had no choice about what SM did/didn’t do for her. She doesn’t owe her anything. And SM didn’t care about OP enough not to break up the family of a 4 year old.

I’d give her the same amount of care and concern that she gave to your mother

It would depend on care she gave you as a child growing up. Did she never cook you meals, do your washing, clean your room, drive you to clubs and activities, make you a birthday cake, treat you well as a child or did she basically ignore you and just do these things for her own child and made your Dad cook and care for you OP? That would determine if I helped a little or not but not with personal care. If this step mum cooked some of my meals as a child. It's hard to think she cooked for her own DC and never gave you a meal too. I might offer to drop her off a home cooked meals once a week. If she dropped you off to clubs and activities I might offer to drive her to a medical appointment occasionally. If she did your washing sometimes as a child Iight offer to pop by and throw in a load of washing for stepmum and make her a coffee once a week at same time I dropped off a home cooked meal for her. That is what I'd do but if she made your childhood unpleasant or never ever cooked for you or did any washing for you I'd point this out to step sister. Also if you want to have any sort of relationship with your stepsister going forward offering just a little bit of help might go a long way. You have sisters who are your family, your step-sister only has you and your sisters. You sound like the only family she has so if be inclined to help her a bit if I could but just once a week for an hour.

And the half sibling is saying her mother raised them, but OP is saying ”By the time my half sister was born I was 13 so the age gap meant we didn’t really have much in common. I went to university at 18 so I didn’t spend much time with her” so OP wasn’t even there from when the half sibling was about five years old so all she really knows is what her mother told her.

agree!

And deeply, deliberately insulting to their actual mother, who did in fact raise them, and made a point of not turning them against their philandering dad.

Yep, and according to the OP a fairer comment would be "She helped my dad out a bit with raising us".

My dad worked shifts and my parents worked out their custody schedule around those... His parents helped out. She did cook most dinners but it was my dad that washed and ironed our clothes, helped with homework, put us to bed, and my dad or grandparents that took us to school. I’m sure she did things I didn’t notice as a child but my dad was very hands on.

So the second wife certainly didn't raise them, and it's rude and self important of the half sibling to attempt to claim that.

And even if it was true (and it's not) they were kids with no say in it so they are not obliged in any way as adults to pay back some imaginary debt they had no choice in owed to the woman her father left her mother for.

Yes, maybe more went on behind the scenes a than the OP realises but if she doesn’t feel her SM raised her she’s entitled to that view. It’s quite emotional language to say you raised a child who is not your own, “helped raise” sounds a lot better than saying raised when OP had two parents.

A lot of me hates the idea of any older person struggling, but I don’t agree with the SS trying to guilt Op into it and think she needs to be firmly told bitching to extended family is unacceptable.

Of course you're not being unreasonable. Just let people know, my mum raised us without much help after he left his family to be with her, and no she didn't raise us. She was ok, not particularly warm, and of course we're not interested in being her caregivers.

It’s a huge ask that’s will potentially massively reduce your quality of life. There are professional carers for a reason.

This would be the civilized way to behave.

I agree with this - you’re not wrong Op. Live your life & don’t give this a 2nd thought.

Personally I would give some kind of bare minimum care because she most likely gave the most care to your father.

How they got to together 40 years is irrelevant, it’s was probably the right decision.

SM might well need care for 10 years or more. You’re right to think hard. Half Dsis is facing a hell of a job on her own.

But presumably she’ll inherit the lot so

Hard agree.

You don't sound cold.
You never connected with this woman and that is how you feel.

Nope.

Not half sisters fault that she is the sole carer, but sure as hell isnt @AnotherPosterUsername and her siblings fault that their father fucked someone else and broke up their family.

They owe half sister nothing.

As for the post about "Do it or you will lose out on the inheritance", be your age! There will be no inheritance to @AnotherPosterUsername and her siblings, care given or not. It will all go to the half sister whatever they do!

As a step mum I think, depending on circumstances, it is unfair to say 'step mum didn't raise us'. I certainly feel like I did with my SC. Shared with their dad I did hair washing when little, baking birthday cakes, tidying bedrooms, taking to extra curricular activities, shortening school trousers, organising holidays, offering emotional support etc etc. I don't know what that is if not raising children and I can't imagine I'm alone. I'm on very friendly, although not really close, terms with them as adults but here's the thing: I absolutely do not expect them to help me in old age. I hope my own DC does a bit, even if it's only to coordinate professional care, but it's never crossed my mind that my SC would carry any responsibility.

I think that is fair enough. You don’t sound cold, it was a complicated situation and you have complicated feelings about it. And that’s all ok.

It’s fine to move on with your life.