Hi Mrs Bucky,
Welcome to the forum!
I'm sorry to hear both you and your brother suffer from depression. While some mental illnesses are heritable or partially heritable, it is often environmental factors (such as bullying etc.) that can elicit symptoms of mental illness. So you are right not to blame your Dad. Depression is complex and identifying whether causes are genetic or environmental (or a combination) is something even doctors can't always get right.
The important thing is that you and your brother get help for the depression. Your brother's self-harming is of great concern, and I am glad you have come to this forum for advice. You and your brother can support each other through this difficult time, particularly because you both experience the unfair teasing and know what it's like. Making an appointment with your family doctor (GP) is crucial. You and your brother could book separate appointments one after the other and go together. I'm glad your parents are aware you both have depression. Sometimes sufferers will hide their mental illness from those close to them, which is unhelpful and can become dangerous if suicidal tendencies develop.
I don't know how old you two are, but I'm assuming you are at school still (please correct me if I am wrong). Telling a teacher privately about the teasing is a good idea, and ask that the teacher does not tell any of the bullies that you have done so. Unfortunately, bullies don't take well to being called out for their actions. I'm sure you're aware of this, but I thought I'd say so just in case! School counsellors can be very unhelpful to talk to as well.
Make an appointment with your doctor soon. It is crucial your brother sees a doctor too, and that he mentions the self-harm. It would be great to hear back from you.
Best wishes,
SM
