Fathers will

My father passed away in UK 23rd of march 2005, to date I have not been given a copy of
my fathers will, my mother is unwilling to give me or my siblings a copy saying everything was left to her, which I know is not true.

My father had houses and land in Galicia, He also brough a house in the UK and made a will there albeit in the short term, his intention was to change it to the same as the spanish one but never got round to it, things get even more complicated as a bolivian national (illegaly working in the uk at the time) married my mother who was 30+ years older than her, and she has not seen him since, she claims she only did it to help him get a permanent visa to live in UK, but I believe it was a ploy to get her money and house in UK. my mother is elderly and I need to sort things out before she dies, otherwise he will get her estate.

I know my father in past conversations was adamant that his half was to be shared equally between his 6 children, but again my mother is unwilling to help us .

What can we do and where do we start