2 doors with separate frames = 2 separate doorways mulled together. This does not equal a 6' opening, except during the rough framing stage. You will have 2 separate completely framed openings side by side by the description given. I have seen the setup I think you're talking about (2 doors in 1 single frame to mimic the look of the patio doors). They took 2 doors and put a working latch & deadbolt on one and the receptor on the other. The receptor door also had a non-functioning handle and a slide bolt on the top & bottom for stability/security when the door was in the closed & locked position. You might be able to have a 3 point locking mechanism installed--check with your builder on this. The big thing that stands out to me when you do this is that it is hard to get the same look of the patio doors. Patio doors like you get from Pella, Jeld-wen, Andersen, Marvin, etc all have a more sleek look because the glass sits in a low profile frame. Most imitators have a bulky plastic frame that holds the glass in place. In my experience, the plastic yellows (even with a coat of paint on it) and the plugs for the screw holes never line up properly. The closest I have been able to find to a door that looks like the real patio doors from the manufacturers mentioned above is the Plastpro flush glazed door. You may want to check them out. If you want to see photos, just ask--we used the Plastpro doors on our house. Here is a link that might be useful: Plastpro Flush Glazed Doors

You can look at a company by the name of Panda. They make a Lift-n-Slide system with a track with a single post that sticks up 5/16" of an inch. There is really no other sill or threshold as the rest of it mounts below the floor. Granted you may not want the expense of a L&S system but this would allow you to use your original sliding door panel idea for light and should also help with sound to some extent

Jed wen aurora doors. Basement to back yard door, garage entrance door, front door and finally door to back yard. Regular swing doors.

We also have an Andersen peoblem Review of Andersen Windows and Doors’ “Big DoorArchitectural Collection” (https://www.andersenwindows.com/windows-and-doors/doors/big-doors). We bought two Andersen “Big Doors” at a price of $24,000 in June 2021. The doors finally arrived at the end of November. They are now installed and span most of the wall of our living room. They come with very narrow stiles, and we ordered ours with brushed-nickel hardware and maple wood finish. If you want a modern, minimalist look it’s hard beat these doors! Alas, they are not good doors. The most serious issue is that they leak. When it rains the water runs across the sill and underneath the doors to an inside channel, where we use a sponge to keep the water from reaching our new hardwood floors. The doors are actually designed this way. They sit on rollers that are raised from the floor, and water can flow to the inside. Andersen uses an aluminum threshold, called a “nose”, to essentially cover up the water. The water supposedly runs off through weep holes, although on ours it stays for days at a time. What do you do if water rises above the edge of the inside channel? Andersen’s solution is a threshold with a 1.5” high edge or “lip” that literally functions as a dam. The lip of the nose protrudes about an inch above the bottom of the doors, so if water ever reached that level, the wood frame would get soaked and ruined. The rail is also a serious trip hazard because it sits right across the opening where you walk. Needless to say, if water can run to the inside, the door is also not airtight. We live in Boston, and we can feel the draft of cold air coming through the bottom of the doors whenever there’s a wind is against the doors. That’s not quite as upsetting as the water, but it is also not exactly what you expect from a door at this price point. Build quality is also surprisingly poor. Our doors came with a poly finish (which we paid extra for), but after two months it is already beginning to peel around the glass (we think from condensation water). We have asked Andersen to fix it under their “best in business” warranty (supposedly including 20 years on the finish), but our request has been ignored despite repeated tries. This gets to the most frustrating part of the Andersen experience: it is almost impossible to communicate directly with Andersen. From deciding specs to handling installation issues,you can only deal with Andersen indirectly through the dealer, which in our case is National Lumber. Our point person in NLwas nice enough, but he had no experience with these doors(very few do as we have discovered), and the technical support we needed from Andersen was never there. A local Andersen sales rep shared an installation video (it’s actually a recorded webinar), but you can’t talk to any Andersen person with technical knowledge. Attempts to contact them by us or by our contractor were resolutely ignored. Long after the doors were installed a rep from Andersen showedup, but he essentially just confirmed that the doors are indeedleaky (“I didn’t design them”), and he refused to answer any direct questions, including the one about fixing the peeling finish under warranty. Andersen is marketing their Big Door Architectural Series as a high-end product, with prices to boot, but their service isdecidedly bottom-end. The design of the doors, while aesthetically pleasing, is problematic. But the lack of support is infuriating. Perhaps Andersen’s makes decent budget doors and windows that big-box outlets like Home Depot and Lowes canreadily service; but Andersen is entirely unprepared to operate inthe upscale market. We made a bad choice. [Taglines: Andersen Windows and Doors complaint; Multiglide; Leaking and drafty doors; lack of Andersen service; tripping hazard; water problem; ignoring customer pleas for help; noservice; will not honor warranty].