Is this legally valid?

I drove everyday for 3 years about 200 miles to look after my Dad who was bedbound and my Mum couldn’t cope. On his death my Mum confirmed our arrangement that I had to give up my job and that I had full permissions across all accounts so that I was not out of pocket. They had joint accounts…now however my siblings who never helped at all want to say the money I used was taken without permission…can anyone please direct me towards the relevant law…I really hope this arrangement is legally respected. My Mum wrote it down after his death so everyone was clear

ANY help or advise would be greatly appreciated…tahnks Tom

See a solicitor.
He will write a suitable letter for your money grabbing lazy siblings.
That’s what my solicitor did for me!