Re: 10" wall installing exterior french doors
The doors will be mounted on the exterior, and you need to fill the "extension jamb: region of the 10" thick wall. I follow that. If you went straight back from the door with a perpendicular jamb, the doors wouldn't open much past 90 degr. That would kind of bother me, and the aggravating fact is that the light coming in would also be attenuated by the close, deep jambs. So, (if you have yet to frame the opening) here's my suggestion. Whatever the trim width in the room, let's say it's 3 1/4" casing, frame a 2x4 wall stub with two studs all around the door, pad out with 1/2" clear ply in place of sheetrock, and apply the stock casing. The rest of the extension jamb would then be splayed out at a 30 to 45* angle to allow the doors to open pretty far, and help the tunnel effect go away. The head extension could be parallel to the floor, or splayed as well. I think I prefer it flat. At the wall, another round of casing would be applied to the splayed jambs as on any cased opening.
Remove not the ancient landmark, which your fathers have set.