can I make clarinets and French horns play for extended periods of time without them protesting against my score for either air or difficulty reasons?
No. You can’t extend any particular instrument. It doesn’t matter much which instrument is most air efficient (it’s probably the oboe), because the greatest need to breathe is often “stale air”, not lack of air.
As air sits in our lungs, our lungs are removing oxygen and adding carbon dioxide to the air. Normally we exhale and inhale again fresh air that has plenty of oxygen in it. The longer the air sits in our lungs, the less oxygen it has and the harder it becomes to extract the oxygen - the air is “stale” and we need to replace it with fresh air.
This is why oboe players actually have to breathe out sometimes when they play. Their instrument is so air efficient that their air becomes stale before they can breathe out enough through the instrument.
Even on clarinet I’ve had to put exhale breath marks in my part sometimes.
The other thing is musically you usually want instruments to breathe together, even the strings should “breathe” with the winds and brass in many cases.
Finally, no matter what you write, players will breathe. You can’t stop them from doing it and you shouldn’t try. The only thing to do as a composer is if there are moments where you really don’t want them to breathe, you can put slurs over those moments and encourage breathing before and after with rests and/or longer notes with no slurs and even decrescendos on them. That’s when we like to breathe.
Pros won’t protest. They might roll their eyes at each other when your back is turned and they will breathe when they have decided it is musically correct.
I’m also remembering that for oboes and brass (especially horn), their chops (aka “face” for oboes) just can’t last through long extended passages. Breath support and embouchure require significant physical effort - not quite athletic level but still fairly tiring. I can currently go about two hours on clarinet (with breaks) but only like ten minutes on oboe. Obviously pros will have more developed facial muscles than mine, but it’s still tiring for your face and core.
Be good to musicians and they will be good to your music.