How do I pay back the debt I owed to my deceased mother?

I am a Muslim living in the UK. My mother lent me £25,000 so I could pay off my remaining mortgage in full. It was agreed that I would pay it back in instalments. Nothing was written down in the form of a contract. My mortgage is now paid off thanks to my mum helping me out. Unfortunately my mother died shortly after giving me the money. I have 2 sisters and 1 brother. My father has passed away also. I have no other family in the UK. What do I do now? When I say 'lent me £25,000' that means she loaned me that money from her savings. Also, my mother did not leave a will. I want to do things in an Islamic way. What does Islamic law say I should do next? Thanks for the response pokhim, I appreciate what the honourable thing to do is, as you say in your answer, but what I actually want to know is what does Sharia law say I should do in this matter?