Can i and my 2 brothers question my dads will which my sister says was left to her?

Yes. Both of you need to contest the Will in question, it may time long time and costly depending on the location of the Will.

You should be able to view the will and its signature to be sure that it is a valid will and that she is a named executor of his affairs. If you are mentioned in the will, then it is fairly clear as to the intentions of the deceased. You may consider consulting a lawyer to make this process more transparent, but, remember that, as executrix, she does have rights and responsibilities and you should honor those.