Advice on executor behaviour

Sorry this is a new account, and for the vagueness, and length. I need some advice, and do not wish the parties involved to google me by the username they know me by or by other specific details!

One of my parents recently died, and named me as executor in the will, along with my sister. Everything was left to the spouse, so nothing really complicated. Only thing is due to the sums involved it means probate needs to be applied for to sort out the personal bank accounts, etc., and that of course means filling in the Inheritance tax forms too.

Now, unfortunately, I don't live nearby and my sister does. I have spent as much time up there as I have been able, trying to get to grips with the extent of the estate, but the more I uncover, the more I am being pushed out by my sister and our surviving parent - I have been denied original copies of the death certificate, have been told not to value anything, and have now been told not to come to the house at all. My sister had our parents firmly in her pocket, not helped by this remaining parent being extremely vulnerable, having had a stroke, and now having memory issues; I know she is quite happy to help herself to anything in the house that she wants, and is being given permission to do so, insomuch as permission can be given....

Now, having seen some of the bank statements, I have just found out that my sister has been receiving several hundred pounds per month from the deceased, paid directly to her bank account by standing order, and this has been ongoing for many years. I believe that any such payments over the last seven years have to be declared on the IHT forms as a cash gift, but it seems my sister wants to have everything wrapped up with the minimum of investigation. Despite agreeing initially to have me handle the financial aspects, she has interfered and second guessed me at every opportunity. I reckon the chattels in question, not shared items, may be worth up to £100K, consisting of a heck of a lot of very low value items with just a few gems, but she wants it all ignored, and all other gifts I know about ignored too.

I understand, from reading everything I can find, I have duties and responsibilities as an executor, even prior to grants being issued, to protect the assets and ensure everything is accounted for. I have spoken with the banks, and the personal accounts will now need both executors signatures to access, but there are still significant sums in joint accounts that I can do nothing about.

Given the sole beneficiary is already effectively in possession of most of the assets, being in the house, along with my sister, whom has a key and her ear, what liability do I have for items going missing or being misappropriated by either the beneficiary or my sister prior to completion of probate? What options do I have to protect things? And do I really have to be worried about accounting for everything, anyway, given there will almost certainly not be any IHT to pay.

This is explained perhaps by my sister being obviously financially stressed... she appears to be claiming means-tested state benefits whilst not declaring the several hundred pounds per month she has been getting from our parent. She complains of having no money, but goes on holiday every school holidays. I think it is the prospect of this money being discovered that is behind her trying to push me out of the situation.

I have no love lost for my sister; we're like chalk and cheese and never really got on, and would normally just ignore her, however I don't want to put myself into a situation where I acquiesce to a wrongdoing, nor do I want to allow her to drain my parent dry, so I can't simply walk away, and in any case, at some point this is all going to have to be done again! Finally, there are an awful lot of items in the property that are financially worthless, but hold a lot of sentimental and historical value to myself, which I do not want to see lost, which is likely as neither of them have an interest in these things.

So... what can I do? If it were a stranger, I'd both report her to benefit fraud and contest that she was not a suitable person to be an executor! But that is likely to drive an (even more) massive wedge between us. And I'd definitely not be allowed back in the house to deal with things...

Thanks for reading...