THANK YOU for this thread! I have two - littermates, boy and girl. I have always been wondering/worried if they are too rough, if there are issues because they are littermates, if this is normal.... etc. They can go SO HARD at each other - and yes there are sometimes those little neck scabs and I was so worried about "drawing blood" (I wondered if that was a sign it was too rough). One will egg the other on until it is a full on crazy wrestle match, they rip around the house, "walrus fight" (mouths open like they are arguing).... everything everyone has said I can say a big DITTO!!! I don't know if they will grow out of this (they are pretty exuberant still, at 1 year and 5 months).
Can't wait to see the other posts!