Hello,
So I currently have a west highland white terrier named Rory who just turned five years old, and an English setter puppy named Sammy who is almost 12 weeks old. We’ve had Sammy for about a month now and Rory has been getting possessive over the water, food and toys, and they growl and bite really hard when playing with each other, almost every time Sammy has yelped. I don’t want either to be aggressive since I have young nieces and nephews that come over often, I don’t want them to get bit.

I have already tried separating them and making them do tricks when they get too aggressive and then let them go play again, and it works for about five minutes and then they are biting and growling again. Also when we pick up Sammy, sometimes he will growl and turn to snap at our faces. He doesn’t mind actually getting picked up, but if he sees something he wants on the ground he growls, snaps and scratches, which almost ended up in him getting dropped on accident a few times. I really don’t want my dogs to get aggressive and have to give one away, any help before it gets too far?

*note: I do not believe in dominance training techniques, or alpha assertion. no ‘alpha rolling’ or even hinting at abusive (hitting, kicking, rolling, flicking, pinching, or anything physical) suggestions please! Thank you for any and all advice in advance!
I cannot say I will always manage to reply to all advice, so in case I forget to say so, thank you!