UK executor - US not recognising UK will

My aunt spent her working life in the US, returned to the UK for retirement. She has a UK will, probate is approved in England, but she has an American bank account and we've realised the US do not recognise international wills. I have to submit a UK tax return as she had money coming in from her US state pension, and I assume some money coming into her UK account were probably payments from the American bank account as well (not many though). I need to pay £12,000 to a US lawyer to get executor status in the US to even be allowed to know how much is in the bank - and I doubt there is that much money in it to break even after that, taxes and transfer fees. Question is, as UK executor do I need to pay this £12k (money I don't particularly have) to make sure her UK tax return is accurate, or can I leave the US bank account be by explaining I'm not accepted as an executor in the US except for an extortionate cost? I can only think her UK tax return might have a high tax rate applied to it if I'm allowed to do this.

Hi ,
 

We cannot advise you on matters involving the USA tax system.  You will need to seek professional advice on this matter. Thank you .

I'm asking for advice on completing her UK tax return. She would have been reporting foreign bank interest in previous years, but I don't have the information without paying a lot of money to find out. Is there a penalty/is it illegal for not knowing this information (given the US doesn't class me as executor)?

Hi,
This forum is for general queries only and is intended to help you self-serve.
We are unable to provide specific advice tailored to individual circumstances.
Alternatively, you may wish to engage the services of a professional advisor/accountant to assist with your enquiry. 
Thank you.