Lori, a lot of people keep multiple garters together in larger tanks. Seems to be more a matter of keeping them separate at feeding time, and yes, you would probably want to keep only one sex together in the tank.......unless oodles of garters is your goal!!
Out of curiosity, Kyle,
How big is your enclosure for the 8 snakes? I'm trying to figure out how large a tank I would eventually have to get to keep my snakes together as I collect them. I'm aiming to have 6-8 in the next couple years.