Kirsch makes them, but they would not be inexpensive.

Most long rods are available everywhere, and not cheap, but affordable.

You'll be buying it once and using it for a long time, think price per use.

you should use a support, Just place it where their will be a natural split.

the door opening doesn't need to be centered with the curtain.

extend the panels beyond the opening, so when they are open, the whole window is revealed.

use a drapery wand to open and close, won't be too long for children.

Do you need privacy, light control? both, I wouldn't layer, just do a grommet rod for easy use.

Bypass C rings I have no idea where to buy them retail

@Rho Dodendron I just learned about this option which is wild after so much research that they never came up in a google search -- I randomly came across the suggestion in a reddit post! This is what I think we may go with. I know builders are making houses with these long walls of windows, how has this not become a more common product!? Ha!

^ try https://www.thecurtainrodshop.com/bypass-c-rings-for-1-rod-diameter-pack-of-10

I found the Remi Adjustable 0.81'' Double Curtain Rod on Wayfair Canada in the Kelly Clarkson collection. Hopefully you can search that out in the US. It is a double rod that goes from 120-170 with what looks like one centre support where the drapes would meet in the middle.

Just like hotel rooms, double rods are available with the use of a baton to have the drapery close and open. These can be mounted on the wall. $107.00

$107.00

https://www.homedepot.com/p/Rod-Desyne-120-to-170-Adjustable-Baton-Draw-Double-Traverse-in-White-BTN99-D/318269419

https://www.wayfair.com/decor-pillows/pdp/vevor-steel-adjustable-double-curtain-rod-fxnu6461.html?piid=100513372

https://www.homedepot.com/p/Umbra-Twilight-Double-3-4-in-Rod-66-144-Nickel-1020562-782/331342256

I have a really old discussion thread (maybe 2012?) where I talk about this.

We have one room in our home that needed a 38' long continuous rod.

We used electrical conduit (comes in various sizes); spray painted it black*, and hung it with brackets and used the "C" rings. (Only needed the "C" rings for the places where drapery would need to bypass the brackets, so that will depend on your set up.)

*In order to paint electrical conduit, IIRC we had to wipe it down with a vinegar solution, spray a primer, and then Rustoleum spray paint.

I've always hung curtains/rods on a limited budget, and it took me awhile to figure out that if there's a bracket in the center, you can attach 2 rods together with a male/male screw. This might let you use less expensive hardware.