My mom has b's... sister has d's maybe double and both my gmas has big boobs and rest of the girls in my family? Why don't I... my sister said that she had b's in 8th grade..

It might be because your still in the middle of lifes changes and you won't know the outcome until your finished with the growth cycle. Also your body will change further should you get married someday and have children. Sometimes genetics skips around and sometimes its environmental. Either way give yourself time to finish growing first.

You really don't want your breasts that big. There are too many problems with big breasts like back aches just to name one.

Heavens sake, you are 14, while some girls are starting to mature, many are not yet. First so your sister did this, or that, you are not her, and your genes are different and you will have a size depending on that, and at your own time frame.

Next yes, as they get older, most hate having really large ones since they can cause back issues, and more.

My mother and sister both have C's and D's, I honestly used to think I took after my dad LOL, I was also very slim (a bit too slim) as a teenager, but my mother and sister always had a plumper figure. I was always an A cup and it wasn't until I reached about 19 that I put on a nice bit of wieght and my boobs grew to a C. :) so give it time and things might fill in.