Family Crisis - Please can you HLP ME!?

Hello my name is sara and well lets just sayt this is a family crisis im only 15 and my mum knows who i am going to get married to so do i his name is imran and my mum said i have to get married to him when i am 18 the man is ok hes alright i would like to get married to him but his age is spoiling everything he is 5 years bigger thank me so i am 15 he is 20 and because of that i have to get married erarly and not do my furtuer plans i want to star work before i get married and have laser eye treamtnment before but all thpse ideas ae gone and plus what s worse is i have to live in his brotjers house we are close but the problem is IAM INLOVE WITH HIS BROTHER TOO MUCH and imagine living with your huband and living with the prson you are inlove with i know AWQUARD but if i tell my mum i do ' twant tolive there then there is going to be a bigg argument i can' take it i want to get married when I am 22 or atleats 20 then if not older but no i have to get married when i was 18 just because my mum got married at a early age 17 i know i couldn'y beliewve it either bit its true i cn never get matried at age 17 i got my eduacation infront of me come on can you and anyway she wants me to be ,ilike her aeraly marriage so please can you give me some advice thaknk you and pkeasedon't say say no to imran becaus there is going to be an arguamnt thank you and soorrrry for my pelling i cannot type very slow so i have to type fast and make eerror mistakes sorrry about that ok . and thank s