Ya know, my grandfather had/raised/breed Weimaraner's for many years, he always had at least one, and a Doberman. Dobie guarded the house, and Dakota was the bird dog. I lived with my grandparents during one of grandpa's dog breeding phases...
I remember one time one of the pups in the litter was pretty aggressive, feeding time seemed to be a trigger point, play time became less playful and the dog would nip at the hand. I was just a kid then, but I remember my grandfather sitting down on the floor with "troubles" and another pup he had an issue with at feeding time, and setting them up separate bowls, and placing one nug of food at a time in each bowl and letting each dog eat only one at a time until they learned that they each would get enough food for themselves, and they quit clamoring all over themselves and fighting, he did this over and over for quite a while...
As it turns out, both the pups were possessive but one more so than the other, with pretty much everything, and as a result, required extra attention, love and discipline, "troubles" always was the "immature" pup and was one of the last get picked of the litter due to its behavior, but before he was sold he was pretty much trained for a puppy and had quit the biting trend
Just a momentary anecdote from my childhood that I thought may help you in your situation...
the feeding trick, it establishes a few things: order for one, it takes away the feeding frenzy and anxiety animals in multiple animal households feel during feeding time that often leads to inappropriate behavior, it establishes you're the boss and they only get food when you say, it shows them they have something that's theirs, it shows them that you are providing for both of them separately and, if you can pull off rewarding them with petting and proper and timely play surrounding and ending feeding time it will show them you care/love them equally as well, the time spent with the animals during feeding (especially at a young, puppy age) will also nurture a really strong bond between you and your animal, that bond should also lend itself handy when training :thumb: