Chad - We resolved this several years ago as we moved primarily to 2-1/4" doors. One could write a book....
I feel we discussed this over the years, with your resistance to relying upon craft, hoping for a kerf in, cut to length fix. Understandable, but not available. My solutions are workable, but not easy. They rely upon top materials and skilled execution.

Please do not use 'head and foot bolts' as made for the mass market. Use good quality (not Chinese) extension bolts as these will work on doors up to 12' or more. Steer away from those gawd awful aluminum sills, especially if you use the mill finish, or worse yet, the brassy ones. Remember, we are trying to make attractive, tasteful objects that often represent the best craft to be found in the house.

If your customer insists on a tinny sounding, dentable and scratchable aluminum sill, then remove the inner hardwood strip and replace it with a wider White Oak Strip. Rebate the inner edge to receive flooring if you like. Make your jig to locate good quality extension bolts so they will throw into the center of the marginal riser on the Pemko sill. T-Astragals can retain 1/2" blades, with the bevel to just under 3/8".

But being woodworkers, I am sure you prefer making your own White Oak sills. We tipped them for a 5 degree slant, with a 2" wide flat at the top, under your paired doors. We used a bronze sill cap on the sill and planned for 1/2" from the meat of the door to the sill. The bronze sill cap was located on the sill to accept the extension bolt. This bore needs to be filed wider to accommodate the seasonal movement of two stiles. Do not just oversize, as it is this point is the start of the whole seal program. We rabbeted the doors leaving 3/8" to cover the gap when the doors were closed (inswing). This left a nice 1/8" reveal between the door bottoms to the sill, same as what was normally seen on the other sides of the door. The gap between the fixed bronze sill cap and the epoxied door bottom was sealed with the brass leaf nailed to the door bottom - later. The bronze sill cap needs a thin bead of silicone full length, both legs at final fitting. Then close the passive door, and locate the brass leaf tight to the sill cap and mark it. This fit is what makes the system draft and wet proof. Take the door down (I know....), and nail the leaf in place, springing it out so when it closes it rubs the top of the sill cap then closes the gap. I often thought of this part as making a door stop for the bottom of the door. And done properly, it works that way.
If after all your efforts, rain still gets in, there is a 1/8" diameter silicone tube that can have a very small bead of silicone run the length, then set into the leaf all the way to make an even more effective seal.
As you can see, some of this can ber done in the shop, and the rest in the field. If your people are setting the doors, you will have no trouble. If others, get drawings and clear instructions and get ready to send out someone to hold hands. You will also find carpenters that modified it all to suit themselves.
This is highly skilled craft with a bit of everything in there - as well as taking large doors down and back up again. Training your people is paramount - support them with tools, carts, space and help so they can do their best every time.
Once a pair is up, with the little fuzzies in place at the center bottom, doors sealed up like this are worth what they cost, and perform very well. Cut any corner, and the whole will be compromised.
And, of course, this is all in my book on Custom Wood Doors. Perhaps you have worn out your copy and need a new one?