Oh, that had to be scarey. I am so sorry. I know MANY will disagree with me, especially the experts, and I respect that. I have always had 2 malts at the same time, with the exception of when we just had Kara (RIP).
I have always had them share their food and water bowl, hoping to aviod any guarding issues.
I did this for a number of reasons. When we would add an addition, of course the pup would follow the leader, that being their new older sybling, and would help encourage them to eat.
Mia and Leo eat and drink together, Leo will begin his meal, and Mia will nibble, and then will go away and come back for about a 20 minute span, to get more. But they start out together.
I know this is all wrong, but it has always worked for me and I watch who is eating what, and how much.
I don't know if this prevents guarding issues, but I never had any. I try and teach them to share everything.
Chewies, is another story. Mia wants Leo's and Leo just wants Leos, but if he even sees that shes in the same room as him, when he has his chewy, he will growl, but if she takes it off of him, which I try and prevent, he just stares. But I am working on that situation.
Same thing with giving kisses to me. Niether pushes the other out of the way, they know to share, one on one side of me and the other one, on the other.
I know this goes against all the rules, but it has always worked for me.
When I had Flakey, and my Tina Marie, had kidney failure, oh heavens to get her to eat, but if she saw Flakey eating, she would join him, even though, she wasn't well.
I just always feared, that if I fed them separately, then they would know, that that particular feeding, was theirs and theirs alone, and if the other went to sniffy the others food, I didn't want the guarding to take place, so I start them out sharing.
So sorry this happened to you, and believe me, my way, goes against all that is taught, but I never ran into a food guarding issue, but it could also be their personalities. I don't know.
I am sure you will figure something out. You must have been shocked. Good luck and hugs.