I was having something similar with Rodaidh and Alfie, at least prior to Rodaidh being stuck in his crate. He is now nearly 16 months and as he gets older he has been challenging Alfie more and more. Alfie used to just flatten him to the floor if he stepped out of line but recently just prior to Rodaidh's surgery I noticed that if their playing turned a bit 'handbags at dawn' it would often end with Rodaidh standing over Alfie baring his teeth, although Alfie can't generally be bothered with fighting whereas Rodaidh has a stronger character in that sense. Rodaidh will also growl and posture at Alfie he he comes near him when he's got a chew or toy but he doesn't do any of this stuff with Tilly and Alfie and Tills never do it with each other or with Rodaidh. I think in my situation it helps that Alfie is so laid back, when Rodaidh starts carrying on he invariably just sits there and doesn't react. I do think it's to do with Rodaidh's age and with him being a more 'dominant' character than Alfie now that he's more physically equal to him he's starting to push the boundaries. Rodaidh is also entire and Alfie is castrated and I wouldn't have said prior to this that either Alfie or Tilly was definitely the 'boss' out of the three of them, neither of them are particuarly bothered by stuff like that and they have never had a go at each other over anything. It's only Rodaidh who seems to be bothered about it although he will not growl at or mither Tilly the way he does with Alfie. As long as none of them are stressed out by it, which so far they don't seem to be, and they get on most of the time, which they do, then I pretty much leave them to sort it out amongst themselves.
