Car audio Help for 1997 Trans am?

My mom bought me an alpine car audio kit from bestbuy and it came with and aftermarket radio, and four 6 inch door speakers. She keeps on insisting that I let her take it up to best buy and let them install it. I have a 97 Trans am. I wanted to get rid of the original audio. Will i be able to use these 4 door speakers and still be able to add 2 12 inch subwoffers to it. I know i need a amp and other stuff but will i be able to add to this set of speakers from alpine she got me? Im willing to just return it and get every thing online separate.
ALso the speakers my mom bought for me wont fit. is there any way i can make them fit in the door?