Sorry to take so long to update this thread folks!
At my last update I had called all the agencies I could think of, including the police, and their advice had been to get a solicitor to sort out the legalities of the sister's actions.
The family at this point were somewhat divided in their opinions - some just wanted to take their share of the money, two believed my aunt's story of the Will and declined their share, some thought it wasn't worth pursuing further, and only two of us wanted to persevere.
In the meantime, the sister emailed all the ones who had asked for their share saying she had their cheques signed and ready to post, only she couldn't now because nasty rotten tremble had reported her to the police. So it went from "I don't want you to take your money" to "tremble has prevented me from giving you your money".
I let things slide for a week or two while I pondered what do to, then called the police again to get a reminder of the exact details they needed. This second call made things a lot clearer than the first. This officer explained that at this point in the situation, any action taken against the sister would be civil action, not criminal action, hence the need for a solicitor. He also explained that the police do not investigate accusations of fraud; they can only act on evidence of fraud. So if the solicitor discovered that the sister had broken any laws in her actions, they would pass the details on to the police. He said that what I said sounded like she had broken a few laws, but I'd need to get a solicitor to prove these points.
The fact that the sister has three times refused to show us the unsigned Will meant nothing, but if she refused to show it, or refused to name the legal Firm that drafted it to a solcitor, that would be considered proof the Will didn't exist.
My investigations that showed the sister hadn't followed the legal process to be Executor didn't count, but a solicitor's investigations would.
Also a solicitor would be able to establish if the decased had a joint account with the sister or not, because if not then the sister has embezzled all the monies from the estate.
So it was clear that there was no way to do this without incurring legal fees, and when I got a quote for the case from my solicitor, I decided I can't really afford to go through the legal expense to get to the truth. If we'd all been standing together and sharing the cost then I would have been happy to proceed, but I knew there was no point in asking the others.
Then I sort of forgot for a few weeks...
But another relative prompted me about it so I emailed the sister saying that despite all the evidence that she is a lying cow (well, words to that effect) I am not going to pursue it any further as she has caused enough unpleasantness, so could she just send out the cheques please.
And oddly enough, no-one has received one yet. 