"He was aggressive with the grandkids", is precisely the story I heard during the re-home process when I adopted my Severe, so in that instance his aversion worked in my favour.
Sorry you're having challenges; it's never good when there's tension between family and flock. That said, I'm of the opinion that it's entirely normal for Solomon to be wary of your grandson (or any other person/situation that's unfamiliar). I remember having that thought about my Severe, "of course he's agitated... unfamiliar people have invaded his home, and disrupted his routine".
I also have a retired racing greyhound who grew up on the track without exposure to kids, and she too is anxious (expecting them to be noisy and unpredictable).
Whether it's kids or garbage cans (my greyhound dislikes walking on garbage day), I believe that addressing aversive behaviours during unfamiliar situations, requires deliberate positive reinforcement training. It's unlikely to cure itself (not quickly anyway), especially in my case when none of my crew have exposure to kids in their life with me.