I think your brother not liking how your gf looks is not a big deal. It doesn't really matter if he finds her attractive or not, he's not the one dating her.
Your mum not liking her on the other hand is concerning. You should find a way to change that if a good relationship is important to you. Has she met your gf? How old are both of you?
Don't cry, don't regret and don't blame
Weak find the whip, willing find freedom
Towards the sun, carry your name
In warm hands you are given
Ask the wind for the way
Uncertainty's gone, your path will unravel
Accept all as it is and do not blame
God or the Devil
~Born to Live - Mavrik~