What can be done about this inheritance issue?

My sister never married and lived with my mum and dad. They have now passed away and I am a divorcee with a mortgage and my other sister is a widow (there's 3 of us). My parents house has been left to the sister who lived with them so she has somewhere to live - it would have been nice to have a third share of the property each at a time when it is needed but now we won't be getting it because the house has been left to one sister - and we were all brought up in the house and I was born there....what can we do?