ANGRY! ( and I've fucked up)

You don't know it's not coming back? He's borrowed it and already has another car. He's taken it Interstate, he can bring it back, it's not on the moon.
You just say to your sister, I had had the car valued as we're going to need the money for the care fees. It's worth £6k what do you want to do do you want to buy it or is BIL going to bring it back so it can be sold?
If your son was going to pay market rate for it, he can pay market rate for something else it makes no difference, unless you were planning to do the same as your sister but she beat you to it

Then your argument about it needing to sit in the drive to deter squatters is totally negated!

I think pp are being disingenuous about POA though -it's to give someone authority to act for you in your best interests, not help themselves to your stuff.

I'm so confused. Has your BIL driven it away and sold it? Why is the car not coming back?

I get it op and I'd be pissed off too. Do your parents have capacity, obviously it may be different in Australia but I was my mums poa and me making decisions on her behalf only came in to play when she was in hospice incapacitated as she had no capacity, until that point she did. Also, same with my mother in law who is in a nursing home just now. She's got dementia, been having delusions and hallucinations but also periods of clarity and the docs etc still say she has clarity. Essentially though, they have gave him the car just borrowed it so it isn't his. Get them to convey this to your sister and say when it's to be returned.

Mainly though, if you both have poa and are executors for when the time comes I'd be thinking it may be best getting a solicitor to be the executor instead (if there is even a need for one) because the fact you aren't even communicating suggests this could cause a lot of issues and trouble later down the line when trying to deal with the estate.

I'm sure your son can buy another second hand car.
Your parents are free to do that even you disagree and had other plans - sorry.

"my son could make them a totally fair offer."

Which by your logic they don't have capacity to aveiro. If they can't give valid consent to lending the car, they can't give valid consent to selling it. So your son would equally be committing theft by your standards

From reading more of the updates my opinion as someone who works with older people who have lost/are losing capacity to make decisions would be that what your sister has done could be viewed as form of financial abuse. Your parents understanding of the term
of the borrowing would need to be understood though. Do they expect the car back ever? Are the car ownership papers now assigned to your sister?

I think I would start off contacting your sister to say that the car is part of their assets, you understand a short term loan was agreed for a trip. Given the car has not returned, you presume they are planning to buy the car permanently so the money can be put towards your parent’s care home costs. See how this lands.
Here, we would be contacting adult social care to look into this as possible financial abuse.
Yes you wanted the car for your son but you have since said you were planning to buy if from them so I think that’s fine.

I think how you feel about your sister is clouding your judgement. It is annoying but it doesn't sound like anyone knew you were going to offer to buy it.

If your sister was going to make your son pay it's value in full, then he's not really lost out.

Similarly, message your sister and ask how much she's paying for it.

That sounds sneaky and unfair. Your sister should have spoken to you.
As others have said you need to go there and check on anything that is yours.
If your sister takes anything valuable remind her (like the car) it needs to be accounted for properly.
I don't know how it works in Australia but in the UK we had to sell all my parents assists to pay for nursing home fees. A car is an asset. POA have to act in the persons best u retests as well or you can lodge a concern with the court of protection (in the uk).

I think you need to separate the issues here. Try to remove the emotional aspect and purely think practical.
Maybe get tenets in to stop squatters.
I totally get the sister thing (I’m in the same position) but the time to have that out with your parents has passed. Your job now as POA is to think only of making the best decisions for them. They wanted to lend the car, you maybe irritated by who borrowed it but it’s ok.
Maybe look at some therapy. It’s really helped me look at things differently.

If you've not experienced something similar to @marmoet you might well say that.

It is not about who needs the car, it is about her using assets she has control of through the POA for her own benefit not her parents’ benefit.

She has blatantly misused the POA not to protect her parents’ interests but to benefit herself. Simple.

I think you are massively overthinking this. Very odd post.

But they didn't need the car they have their own? Guaranteed you won't see it again they will say ohhh it's broken down sign here give us permission to selling etc etc 🙄

I've had a similar upbringing with my sister unfortunately she can do no wrong and if she does it's because she didn't get the chance to have children (makes zero sense) or "you know what she is like" (fucking hate that sentence) now our parents are elderly and getting distressed because she isn't around because she "has a life" (I apparently don't have that luxury) I made a point to back right off from my mother my father is not so bad now because it affected him when he was ill recently he was able to see the difference between us both

I understand OP, you both have POA, none of your parents need the car. That car would, eventually, be part of the inheritance but she has taken it without consulting you. It is not exactly theft but, it is grabby. This is something she should have at least discussed with you before taking the car away (and depreciating its value with such a long drive).

Forget about tiptoeing at home, doing the garden, etc. That is part and parcel of not being the golden child and there is nothing you can do to change that. I would try to put this behind me but keep a watchful eye in case she decides to use her POA to her own benefit again (as she has already).

I think the house and car should be sold (possibly to son) ASAP and put into their accounts. And I would be wanting vision of those accounts to ensure that no one is taking money out that shouldn’t be. Then it’s clear and no one can argue

You are annoyed because you didn't get the car?

Get out of jointed poa. Leave it to your sister to deal with if you aren't happy to do it.

@marmoet I think many posters are being very harsh.
I understand where you're coming from.

It was wrong of them to ask very vulnerable people to take the car. They have their own cars.