looks like you are going to have to start feeding them  multiple times a day
in smaller portions
My cats are like this  I end up feeding Rumble who eats a few bites and
leaves the food and comes back to an empty dish due to the rest of the hogs.
I have to feed him a few more times a day  I usual take a dish in with me
were I am or he is and put it in front of him.

The best solution I've seen to this was someone who constructed a box with
an opening that only the thinner cat can fit through, and put that cat's
food in it.

Your problem is easy to solve with no headache or diving into cat
psychology.  Cats didn't survive all these years by being picky.  Put the
prescribed amounts of food out for 20 minutes each day.  That will become
feeding time to your cats.  They will program themselves for this.  The cat
that will only eat 2 bites of food may do this for a few days.  I promise
you that when it is necessary for the cat to eat more food it will.  You are
letting the cats run your life, you must tell them the way it is.  They will
eat and they will survive.   This is very similar to when my vet wanted my
cats to eat a new medicine type food.  For nine days one of my cats thought
if she refused to eat the medicine food I would bring back the old food.
Yes, I said nine days my cat tried to tell me what should be on the menu and
did not eat a bite.  She finally realized that the new healthy food in the
bowl was the only thing it would ever be.  She broke, she ate, and the vet
recommended food is no longer an issue.  If I listened to most of the
nitwits here I would have spent a year messing with different foods, mixing
and negotiating with the cat.  And the cat would have probably been dead
from the infection.  I dealt with it via tough love and we moved on.  Feed
your cats once a day.  Your two bite cat will quickly learn to eat enough.
The reason it eats two bites is because the food bowl is always there,
because it can.  It formed its own habit.  In the wild the cat would
experience nothing close to that convenience.  So no, you are in no way
close to being mean or hurtful.  If anything you are bringing the cat a
little closer to its natural ways.  But I might add that the certainty of a
meal once a day is even quite better than anything the cat would experience
in the wild.  The 2 bite cat would not even be an issue to myself.  Do as I
say and the cats will be fine.  Your over eating cat will get the required
diet, and the other cat will eat what it needs to.

Oh I might add that I hope you read this quick.  For some reason my posts
seem to get deleted from this forum.  I don't think I post anything too
vulgar.  And I assure you I would kill to save my two cats.  We sleep
together, play and one is like my shadow.  Follows me everywhere like a
little puppy dog.  But with so many issues here, i tend to view and deal
with them in such a simple way.  I just can't over complicate things as i
often see it done here.  The moderator (or someone) here seems to be jealous
or something that my simplified solutions have success.  So in advance I
won't be suprised if this, and my last posting soon vanishes.  I am sure
that my (feed once a day) recommendation will be deemed as inhumane or some
other bull.  So all I can say is I tried and I hope you get thru the
problem.  Keep it simple and you will.