Hello. Thanks for writing in. The nibbling is most likely a behavioral issue. It could be due to affection but most likely has to do with social heirarchy. Often dogs will nibble or lick on members of their "pack" that they are referring dominance to. Sometimes they use it as way to get closer to the more dominant member of the "pack." It can be a way for them to relieve anxiety also. They do consider you a part of the pack. It can often be a behavior that gets annoying. The best thing to do is to redirect their behavior to another chew toy. If they are nibbling on you, pretend that it hurts and walk away. It lets them know that behavoir won't get them attention. That is what their litter mates did when they may start playing too rough. You can redirect their attention to another chew toy as well in this case. Please let me know if you have any other questions. Hope this helps.