older brother, younger sister

Question
I have a 10 month old dog who we have had for 6 months and we just got a 4 month old about a month ago.  The 4 mongh old is a very playful dog where as the older dog is very calm.  She loves being around her big brother, so much that she crawls in bed with him when they are sleeping.  We just moved her into our room to sleep about a week ago and during that whole week, every morning there would be a mess to clean up.  We figured that it was the younger one so we put her back in the bathroom for the past two nights and found out it was the older dog.  Do you think that his going to the bathroom in the middle of the night has to do with maybe him being stressed because he no longer has his bed to himself?  And if that is the case how do we stop that behavior and are there any ways that we can teach her to stay in her own bed and not bother him during the night?  i don't want to keep her in the bathroom forever but i don't want to punish him if he is stressed because of her.  Help!!!!  Thank you so much.

Answer
Hello, Raquel. It's difficult to say for sure, but it sounds like your older puppy is feeling a bit 'threatened' by the new one, and it could be that what he is doing is marking territory. I don't think it's necessarily due to >>stress<<, but it probably IS due to the fact that you just started letting the new puppy sleep in the bedroom with you all and he is trying to ensure that she knows her place, by marking the room. If it were me, I would crate him at night for a while, until he gets used to the idea of her being in there, too. If you don't feel that's fair, you can crate her in there as well, but if she is not making messes or tearing things up, then there is really no need to.