Families during the assessment process

Hi. I'm 21 and currently undergoing the diagnostic process for ASD. I've always been shy/distant/what some would describe as emotionless/bullied/like routines/have weird interests/lose my temper over stupid things (destroyed various items in the house as a result) etc

Anyway, my problem is, even though I'm undergoing the diagnostic process, people such as my dad and brothers are saying I don't have ASD until I'm diagnosed with it. My counter is that if I do have it and do get diagnosed with it, I've had it most of my life so their argument is invalid. I mean it's causing a lot of tension and causing me to be upset, and I don't know what to do in this situation. Anyone have any advice? Thanks.