Layla is 2. She's just as you described. Grim is the one you described as an alpha. He steals nothing. He doesn't try anything with any dog. He's respectful of the old gal. I don't know if Jade 'learned' how to steal from Layla or what. She used to be the calm steady one. Things have changed. Took her to the vet about it. Vet thinks she's mentally slipping a little. We're watching her closely.
Layla has only ever learned 'sit'. She never did get 'down', but not for lack of trying.
In your 1st post you said Jade took something from Grim and you took it and gave it back to Grim.
You enforced his status at that point as being higher than Jade's. That's why he felt within his "right" to steal it back when she stole it the 2nd time.
Now, if you didn't want Jade to have it, that's fine, but don't give it back to Grim, because he's a puppy and it's "natural" for the leader/alpha dogs or higher in status, to steal puppy's things.
That's how puppies learn they are lower in status than the alphas.
So if you want him to have something that's exclusively his, give it to him in a crate, or separated, but don't take things from the leader dog and give them to a puppy (if alpha/leader has stolen).
You have to take an active role in maintaining the leader's status, if a senior, because letting PUPPY take over the house is not good.
Now, the Pug is also leader over Grim, because she's been there longer, she's older and
she's a female.
I'd do this, regardless, because it's good
, mentally for puppies to be underlings.
I don't care if he gets to be 100lbs, he needs to see himself as the last guy on the totem pole, because he'll be easier for you to handle and you'll have far fewer issues.
You do that by separating him at times, crating when the others aren't, and not worrying if they have gravy on their food and he has none.
Dog's don't view their lives as "fair", so we shouldn't worry about it either.
My "alpha" boy goes places with me, this enforces his status, along with his attitude that he owns the world. I have a female "true" alpha as well, and you'd better bet I don't take things from her if she's got them, and give them to other dogs. She's also the oldest - and if she wants a particular bed, I don't make her move so someone else can lay there.
Now - fostering can be different, and yesterday one of the fosters thought she'd guard a bed she had from a foster who has been here since last summer (Candy's only been here since last month). I promptly made her move and in fact crated her for a few hrs.! She doesn't get to waltz in here and guard things when someone else is older and has more rank.
I guess my point is, take a more active role, you said you're not, and that's how it would be "in the wild", but then you actually did be active in taking something Jade had stolen and returning it to Grim. It's fine to not allow stealing but (and this is how I'd handle it here) don't give the item back to the owner because to a dog, you just demoted her and PROmoted the puppy.