Hi Sue
I don't blame you for feeling scared. That is a lot of cancer in a short time. My eldest sister was diagnosed with breast cancer 3 months after I was so we had the genetic testing. We were told at Peter Mac that it was the youngest effected person who should have the testing so I would expect they would want to test your younger sister rather than you. I was tested on behalf of our family. Maybe different places have different ideas on that.
Although I tested negative for BRCA1 & BRCA2 there is still a lot they don't know. There could be still some family link or it could be a coincidence that we both got breast cancer. Our other sisters have all had mammograms and ultrasounds as well.
Don't feel selfish about being concerned about yourself and your children. It's only logical and natural. One of my sisters said she felt guilty about not having cancer when we did. That's understandable but also unnecessary. It's not anyone fault about who got cancer and who didn't.
When I was diagnosed my eldest sister said to me that she wished she had got it instead of me. I found that an annoying thing & thought (but didn't say!) that I wished she had got it instead of me as well. I still feel a bit guilty about that thought. Of course, it turned out she had cancer in addition to me so that was even worse.
I'm sure your family appreciate whatever support you can give them, over the phone is still support.
Best Wishes