Hi,
Your Dad has probably had his emotions badly rocked by your breast cancer, especially as he lost his Mum to the disease.If he does not deal well with emotion he has probably never really processed his grief at her death, and now is both reliving losing her and fearing losing you. He may think (as my mother did) that you were blaming him for your breast cancer. So maybe tell him that even without this gene, more than one in ten women get this cancer, so it is not an unusual thing to get.
( He also needs to know that he and your brothers are also at higher risk of getting breast cancer, yes men do get it, and it is a higher risk for men with the gene than otherwise)
You might like to explain very gently to your father that knowledge is power. And that while he may be genetically responsible for passing on this gene, there is absolutely no blame to be laid on him, and he has nothing to feel guilty or bad about. No more than if he passed on a gene for brown eyes instead of blue. And no more than you have to feel about your own children's risks
You could explain to him that it is helpful for people who have a high chance of having this gene to know whether or not they do. They can then manage their risk carefully and wisely, and get help from knowledgeable medical experts on their best options. Some choose to have children at a younger age and then to have surgery to reduce their risk of breast cancer, having breasts and ovaries removed. Others are meticulous about having annual mammograms and scans.
It is hard enough dealing with the impact on you without having to handle all the problems that go with dysfunctional family members.
Re implants vs transplants, it can pay to get two or three opinions before deciding what to do. And do join Louise Turner's Breast Reconstruction group in BCNA: she sounds really lovely and is running a brilliant group that would be the perfect place to go to for all the answers.
Best wishes,
Jessica