Shapeshift

Prologue of Part 1

My family and I are Sakalas and we are, like any story, not normal because we have powers but we aren't heroes or villains because there is nothing to fight in England and superheroes have unnecessary outfits, like why do they need the whole super suit if they just need to hide their face.
But how did we get powers? The story is vague as my great, great grandpa was a kind soul who decided to climb up a mountain as he saw this as his calling in Africa. This particular mountain had a mirror with our last name "Sakala" on it (a reason for that is still unknown) and an ancient book. The strangest part was the mirror started talking about how my grandpa was chosen to bear the power of the book and those special powers can be passed down from generation to generation, including in-laws.The book had the power to archive our magic in it, with the name, advantages and ways to be improved. The mirror gave advice to all who seek wisdom from it.
That was when he realised it was the beginning of a new opportunity for our family. We were sworn to secrecy and didn't tell anyone about our powers, the mirror and the book and my grandpa was labeled as the guardian. He passed it down to his son, who passed it to his son, who passed it to my grandma who is very soon, going to pass it to dad, who was meant to pass it to my older brother which is where the confusion happens.
I had an older brother and it's unclear to me how he passed away and why my parents never talked about him or his power - maybe because talking about it makes them really upset - so I don't question it further. The whole events happened before I was born and before my parents moved to England.
That leaves me as the next guardian but the age I realised what my grandma really thought of me was five. Dad told me that when I was born, he couldn't predict my future - he has mind powers- as it was all static so did I even have a future? He didn't even know if I was going to have powers or not. Were my powers blocking this? The mirror confirmed none of this was the case and could never get powers.
I properly learnt that my grandma didn't like me after my younger brother, Matt, was born four years after my birth and he had powers of athletics so he could run really fast, he was very strong, he could jump very high and he had super regeneration - I learnt he had regeneration the hard way-. Grandma was overjoyed and I heard her tell mum and dad that Matt could be the next guardian but they disagreed. It hurt the fact that she didn't believe in me.
I loved my brother, nonetheless, and we often played heroes together and pretended characters we saw on TV were real and with us. I even borrowed some character traits to make me more loveable to Grandma but she didn't care.
They keep thinking I don't have powers when I do. What I want to know is how and why. That power is Shapeshifting. This whole story gets crazier from here.