How to be top dog? 2 year old Staffy is trying to rule the roost

I have a very cute little rescue Staffy, he is nearly two and I think we’ve hit the terrible teen stage, he’s starting to ignore me and nipping people’s feet and recently he’s started jumping up at me and trying to nip my arms.

I think he believes he is the alpha dog, how do I convince him that I am not to be messed with??

So far he is put in his crate or a muzzle when he gets to nippy with my friends and when he gets really too much I crouch over him, so my knees are on the floor and I’m sat on my heels, then I put my elbows and hands on the floor and use one hand just to hold his muzzle to the floor so he can’t nip my face. I wait until he stops struggling to escape and his breathing relaxes. I don’t know if this is effective though.

He knows my mum is top dog because when she yells “DOWN!” he squats by her, ears down, tail wagging, licking his lips and being generally very submissive but even if I take the exact same tone of voice and body posture he ignores me.