* 4 speakers total: Two in the front doors and two in the rear deck.
* Size: Most likely 4" or 5.25" speakers in the front, and potentially smaller speakers (4") in the rear. It's possible some models had the same size in both front and rear.
* Brand: Unbranded, generic speakers typical of factory installations. No specific manufacturer was prominently featured.
To know for sure, you would need to physically check the speakers in a 1999 Chevrolet Prizm. Looking at the speaker itself might reveal a manufacturer's marking, but it is unlikely.