My chihuahua gave birth to pitbulls?

We work with a rescue and we were fostering a long haired chihuahua about 3 years old. A few days later we found out she was pregnant. She had them about 3 weeks after we recieved her and she had a terrible time with the labor. She ended up being in hard labor for about 5 hours but finally had her litter of 5. I am concerned because were not sure what got her and they really look like pitbulls. 2 are brindle and 2 and black and white. the runt unfortunately ped away. They are growing at rapid speed and they are only 8 days old. they look like pits but im not sure if they just look like that because they are puppies and maybe their features will change. i dont know, ive never had puppies before. im just concerned and a little curious. any information would be great also as to when they open their eyes when they get teeth. what kind of teething toys things like that. also im concerned because the oldest and biggest one is very aggressive while nursing on the mother and im not sure if thats normal. any information would be great. thank you