Good news! Brodie has been eating normally in the kitchen for the past few days, with only minimal staring at the front door. Some of this is probably due to post-Halloween anxiety wearing off, but I have also determined a few other factors coming into play and hence been able to adjust some variables.
One is that the youngstercats are probably pretty close to being full adult size at this point. This is somewhat related to what Matt was saying about the cats (and specifically Brodie) eating when they are hungry. Of course it is still important for cats to eat a proper amount of food (for their age, size, activity level, etc.) daily and cause for concern if a given cat refuses to eat at all for more than 24-36 hours. But for them to want food at less frequent intervals as they get older is pretty normal.
I've actually discovered recently, by way of offering dinner 1-2 hours later than I had been previously, that Brodie knows how to ask for food. His technique is to come up to me (especially if I am standing in the kitchen), gently brush my legs with his tail, and then jump up onto the mini cat-tree thing by the kitchen window and meow. Apparently there is a point at which he gets peckish enough to be more interested in his plate than in whatever is going /on outside the front door.
Shadow and Cora would have been fine keeping the old, earlier dinnertime (both of them have always been a tad more active than Brodie) but they've been good sports about switching, and the transition has been smoothed by my offering them some of their daily treat allotment before the meal proper. This way I get the logistical tidiness of being able to feed all 3 cats at once and nobody is in a position to be wondering why their sibling is getting food when they're not, etc.
Of course if I absolutely had to I am sure I could work out a way to feed folks at different times, and I am sure the cats would adjust fine to that given the opportunity, but I appreciate being able to just have a scheduled mealtime as that condenses the monitor-and-cleanup stuff into one small interval.
The other thing I've come to note is that Brodie seems to appreciate it if I guard the front door on his behalf. As in, he spends a lot less time looking up while eating and startles less frequently if I sit somewhere between him and the door. My house has a rather long, tunnel-like layout in which the front door leads straight into the living room, which in turn is open to the kitchen (and the kitchen opens to the back yard). So I can sit in front of the dining table or on the couch and from there be able to see the cats eating and monitor the front door as well. Works out pretty nicely! Though I have to wonder if this task (dinnertime door-guarding) is something Nikki would be interested in taking over...Brodie likes and respects her a lot, and she is Security Cat, after all.
So, yeah, for now, looks like we are back to peaceful and logistically easy suppertimes for all the kitties here. I've been told I "tend to over-analyze" things and perhaps some of this kind of writing will strike some people as evidence of an overfocus on minutiae, but the way I see it, there's no such thing as an irrelevant detail when it comes to cats! Plus I figure Brodie can't be the only sensitive dudecat out there, and thus perhaps someone dealing with a similar thing could benefit from reading what's worked in our household.