I have an 8 WK old male puo.my friend has the brother.I have had mine since 5 wks old.too young I know.but if I didn't buy it a homeless man was going to. Anyway .the first time they met up again was last WK in my back garden. And my pups brother kept attacking my pup in an aggressive manor.we just reintroduced them today again for 2nd time,on a field which is next to my house and my friends house who owns the brotherwe unleashed pups and my pup was aggressive and actually started biting his brother .it scared me as I have never seen him be so aggressive. The brother saw his mum earlier on today whilst out for walk and the brother suckled the mums milk for bit. Could my pup have smelled the mum on his brother . it was also the 1st time my pup went to the field where as the brother does go there daily.I also have a 10 yr old staff but my pup only plays with him and doesn't act aggressive.. He annoy h only by nipping him .trying to play .plz help thankyou .ps the brother is bigger than my pup.