Triple Door with Transom Threshold Question

I have a 3 door (36") opening on the side of a sun room where the jambs are rotting. I am confident I can redo the "composite" door unit and rebuild the transom frame, but I'm unsure what to do with the threshold. I really don't want to pay 10k for a prebuilt unit. The way I see it, I have 3 options:

1) Pay for a custom door to be built 10' wide with the transom
2) Recreate the door unit/rebuild transom and install on top of existing threshold
3) Same as 2, but replace threshold.

I'm inclined to go with #3 while I am ripping it all out, but getting a 10' threshold seems scarce. For the dummy doors on the side, I don't care too much what the threshold does as long as it runs away from the house. For the active door, I'd like to buy a prehung, but I assume I will need to remove the included threshold and adapt to a new one? If the new threshold has a continuous raised area for the sweep, will I need to notch this for the jamb or the other way around? I need to tear a bit more up on the existing door to see how it was done before. The 5/4 framing holding the unit together goes all the way down to the subfloor, so the aluminum must be notched somewhere, I just want to plan it out before instead of day of construction. Based on the second photo, is it possible the thresholds are individual and then there is an extension that locks them all together in the front?

Door unit

Continuous threshold

View of damage and how it is constructed

 

Also, is there an official name for the fixed doors on the sides?

 

Your current door has a continuous sill nose. It's a separate accessory that clips into a notch in the front of the aluminum door sills. (On doors that HAVE the notch for it) So you can set all 3 doors (and 3 transoms) separately and if you have them aligned perfectly, you would cut the sill nose to length and clip it in last. You have to do that before you install any of the exterior trim, since the exterior trim sits on top of it. And in order to remove the existing sill nose, you would need to remove the trim, cut any caulk in front, then pry the front edge of the sill nose upward until it unclips from the sill.

The fixed doors on either side of the operable door are just 36" prehung sidelights.