There are two ways to approach this:
-1- Trying to get a perfect fit: If you're going to be showing, doing long rides, performance riding, etc you need to be pretty close to a perfect fit. It can take a lot of patience and sometimes luck to find the perfect fit. Sometimes can be pretty expensive too.
-2- For just hacking around and enjoying a nice ride, when a tack-store, saddle-fitter, funds, etc are not readily available, sometimes we find ways to make do the best we can with what we have and find ways to make a horse comfortable.
It sounds like right now, you want to make something work for now.
I'll look at the grey horse first:
The fit up front along the shoulder and wither looks pretty good. The tree angle seems to be a pretty close match to her shoulder, and you have a nice pommel-clearance. The panels are supporting her in the right place.
When seen from the side, the saddle seems pretty balanced, but the rear of the addle comes up really high off her back. This indicates to me that the saddle has too much rocker for her fairly straight back. There is nothing you can do to correct this. Imagine a rocking chair on a flat floor. It will never be stable, and will always have a pressure-point at the lowest point of contact.
When seen from the back of the horse, the shape does not match. The saddle has gusseted panels, which makes then have a flat profile for a flat-backed horse. Your horse has a nice slope to her back. What you end up with is that only the inner 1/2 of the panels is contacting her back. that means all your weight is being distributed over a far less surface area than it should be. There really is no way to fix this problem either.
Verdict on the grey: I can't see any way to make this saddle comfy for this horse. She needs a saddle without gussetted panels, and with far less rocker. Your tree angle and gullet-width are pretty close.
Next the bay:
From the front: The tree angle doesn't seem too far off, but the tree is too wide. It sits down too far on her withers, and the panels sit on her shoulder too far down.
From the side: The pommel is clearly too low. The saddle is not balanced, but tipping forward. If you were to canter in this saddle, you'll feel like you're about to be pitched over her ears. The rear of the saddle is also off this horse's back. I'm unsure whether this is due to the saddle being too low at the front, or whether the rocker is too much for this horse as well.
Can anything be done to band-aide it? Since the tree-angle doesn't seem too far off, but it's just plain too wide, you could try to put a wither-pad or front riser-pad under there. Or as Unclearthur suggested in another recent post: Fold up a handtowel and place under the front of the saddle as an inexpensive test. Now see what the panels look like at the back. Do you have contact now or are they still up in space? The pics where you have the black pad under do look like they position the saddle quite a bit better at the shoulders, withers, and balance the saddle better.
From the back: Having seen another picture of your bay from the back, I can be pretty certain that the gusseted panels are the wrong shape for her back as well, and there is likely far too little contact with her back to support her.
Verdict: this horse also needs a non-gusseted saddle, and a tree slightly narrower than the grey needs. Unsure of whether you need less rocker as well.
Can it work? I don't think it can for long rides or in the long-term. Do the test lifting the front of the saddle a little, and re-evaluate. It might work for the short-term until you find something else with some correction at the front, or if you plan on the bay filling out a bit.
I'm assuming you're hoping to get a saddle to work for both horses for now. They are pretty different, but not night-and-day different. If you really want to somehow make do with one saddle, make sure the saddle is wide enough to fit the grey. Then you fill in the front with front riser, wither pad, etc on the bay. You can't get a saddle that's too narrow for the grey - nothing can be done even temporarily to relieve that problem.
If you are looking for a perfect fit or a good, long-term "keeper" saddle, then this saddle will not work for either horse, sorry.
If you want to use the same saddle on both horses long-term, you may start looking into the adjustable gullets.
Another suggestion, coming from a lover of all things Passier, is an older medium-tree Passier (from mid-'70'3 to mid '80's on the PS Baum tree). The tree-points are very short, so they're pretty forgiving if the fit isn't perfect. The gullet is generous. They have a cutback pommel to clear the withers. I ride many different horses (not mine), and between my old Passier and my new Thorowgood T8, I can work my way to a respectable fit for most of them. Looking at your pics of your horses, they are very similar to horses I ride that my Passier has worked well for. Be aware that the older ones can have lovely flocking, but sometimes it's rock-hard and lumpy too, so be careful. They are not gusseted, and have a moderate rocker.