Recently, I acquired a new bullmastiff(luna), the sister and littermate of my original bullmastiff(Loki), when they first met Loki snapped at Luna for which she was adequately corrected for, they then went on a walk together and later that night both allowed into my home together, loki quickly set about asserting her dominance with multiple telling off, leaning on, placing head on top of Luna. Today is the 4th/5th day and they seem to be getting along great will happily sleep next to eachother walk nice next to eachother on walks, etc. And, I have a few questions on body language and was open to hearing peoples thoughts on the matter, Loki constantly wants to initiate play but I'm in two minds whether she is initiating play or harassing the new arrival, albeit they sleep alot so its not constant. Luna often licks Lokis mouth, when loki does tell her off she backs away immediately. Now here's the question when they ruff play outside(I only allow them to play fight outside), Luna the new arrival is larger than loki and can use body slams to her advantage and will growl a fair bit(all normal), I'm just use to loki not growling at all she will literally only ever growl if engaged in a proper scuffle with a strange dog for example. But when loki is playing with Luna her hackles are often raised and tail straight out which tends to either suggest loki is looking for a fight or is trying to dominate her, but they both keep going back for more and seem happy enough, so the question is am I reading to much into it and they are playing happily(never blood drawn or scratches or either dog running away yelping,etc.) Or is loki trying to establish dominance, opinions would be welcome. I have tried to attach a video for a clearer picture of what I'm on about but the file upload is to large. So here is a picture of both.