Sounds like our house. Gracie Ruth is 7 months older then Yogi, yet they are the same size...Yogi is just a bear.
They are constantly playing and "fighting" and oooohhhhh the noise they make. You'd swear it was a pack of wild Yorkies tearing the flesh off of some poor prey animal they just killed.
Occasionally a yip comes from one or the other. But they are quick to stop and start sniffing each other as if to say, "I'm sorry, I didn't mean it, are ya ok?" Not 2 seconds later they'll be back at it or side by side eating a snack or laying down for a nap together. Sometimes it sounds really serious and I have to look over and they aren't even touching each other, just laying facing each other nose to nose tossing their head around and make an awful racket. Occasionally, but rarely, they are serious. They are quick to stop when hollered at to Quit! But mostly it's just full on hard puppy play.