I'm admiring RedAndWhiteBlanket's tenacity on this one
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It does sound as if the parents have funds and they could have done a number of things, which OP isn't entirely clear on.
There are two main roles they've possibly designated: Firstly, holder(s) of Lasting Powers of Attorney which give the holder the power to access and pay out the donor's funds (LPA finance) either alongside the donor while they have capacity or when the donor no longer has capacity, so: pay bills, ask banks to release funds as needed. To make decisions about care support and medical treatment, someone needs a LPA health and welfare, only to be used after the donor has lost capacity. Both LPAs must only be used in the best interests of the donor(s).
The can also appoint a trustee(s) who can oversee a financial trust of some kind, or an inheritance in the longer term and make decisions about how money should be appropriately distributed.
The two LPAs and trustees can all be different people or all the same person.
My experience is: I held both types of LPA for my DM, and I have given my own LPA permissions to my solicitor's firm (finance) and friends (health and welfare). I'm 61 and have no children or relatives.
My solicitors won't take LPA health and welfare, I understand solicitors normally don't, and I can't imagine how solicitors could fulfill that role in any case. They will access and use my finances to pay bills in the event I lose capacity. The decisions informing the solicitor on how to pay out funds will be made by: me in a guidance document, by my friends in various scenarios (and I've made a separate guidance document for them) and the various people who would submit bills or might have input as e.g. HCPs.
So the solicitor is just a professional person with authority to administer bank accounts and similar on demand. The people who have to make the domestic and care decisions are the parents themselves (including in advance instructions and statements of wishes), LPA health / welfare holder(s) and / or family i.e. daughters and DiLs, and adult social care and HCPs.
It depends on what combination of roles the parents have designated as to what input OP and her brother will have. They may be asked to make some or all of the domestic care decisions without having the power to administer the funds (and yes, solicitors will charge a good whack for doing that), or another unknown person or body may have been appointed to oversee support and care etc. and / or to make longer term judgements about how to use or distribute the parents' funds. Unless the parents explain in detail what they have done, it's not an unburdening of the adult children is it? Of course, it may not be possible, in reality and down the line, to fulfill the conditions the parents initially wanted: adult social care and HCPs can be the final arbiters, as can soaring care costs.