The important thing with bringing a new puppy home to an already existing pup, is that you keep the pack order intact. So, today we made sure that Dakota stayed on her Sunday routine of a morning walk with my husband and her morning treat of doggie ice cream. (Yes, we do spoil her) By doing this, we ensure that Dakota knows that Cheyenne is not going to take away from her and she is not a threat. It is difficult to keep you eyes on two at a time and we did have to decrease the size of their play area so that they couldn't sneak off behind a cabinet or anything but we know that with time things will get easier.
(laugh) I remember when we first brought Dakota home - she was 8 weeks also. Within 2 days, I was in tears and exhausted. Had the breeder not been 4 hours south of us, I may have tried to take her back. I was working full time, doing everything around the house, going to graduate school for my MBA and then taking care of a puppy. It was so hard at first but as soon as the puppy learns the routine, everything starts to work itself out. Yes, it is crucial that you make and keep a routine with your new pup. This includes eating, sleeping, potty breaks, walks, play, and so on. Dogs love schedules and once you deviate from the schedule, that is when things turn bad.
You also have to maintain the pecking order. Dakota plays very well with Cheyenne but she was getting a little too rough at one point. So, I refocused her immediately instead of yelling at her. First, I had her sit, then make eye contact with me (forgetting about the little chocolate ball running around the room), and then when Cheyenne was far enough away across the room and not even knowing we were in the room, I had Dakota roll over and give me her belly. You see, I am alpha in this family, my husband is beta, and then Chi (Dakota), and Delta (Cheyenne). I reinstituted my role in the family and had Dakota submit to me to remember that I am, indeed, the alpha, and that she may be over the pup but she has to play by my rules. This worked well but if you decide to do this, make sure those that are below the pup, in pecking order, are away first. If not, you will confuse the pup you are working with and also allow the other pups to see this one being submissive and therefore allowing the new pup to think that the old pup is submitting to them. Big no-no! Maintain that pecking order - remember that if you treat your dog like a human, it will start to treat you like a dog. Dogs like and are more comfortable with being a dog and therefore should be treated as such. At least, this is what you should do if you want a happy home, to be able to sleep normally again some day, and a good and healthy relationship with your dogs.