Is this normal for two kittens? ?

I got my first kitten at 6 weeks old and since he was 9 weeks old I thought having a friend for him would be nice so I got his brother and now there both 10 weeks old but they are fighting is this normal? At first my first cat hissed and put his back up but then they just started fighting I'm not sure if there playing but they bite each other, I feel bad for the new cat cos he is so layed back and only fights back he just wants to lye down. Will they be friends or just keep fighting like this? Thanks x