Thank you for your opinion princecharlie. It always makes you feel better to hear someone else's thoughts. My gut tells me they are probably playing too since they are littermates (brother and sister from the same litter). They are only 8 weeks old, so that may be why they are so rough. It probably wouldn't freak me out so much if one wasn't twice the size of the other. I just keep thinking she is going to hurt him -- the sounds they make are really awful!! I'm sure it will get better. I guess I'll just be refereeing for a while.
Thanks again.