I just listened to all movements. First, my sincere respect for you both since I know that those Brahms sonata aren't easy, neither for viola (that would not be my problem
) but too for piano. My cousin plays the viola too, professionally, and asked me to do a Brahms sonata. I refused since I would not have time anymore for other solo things (and opted for an easier Schubert sonata instead).
First impression: Overall well done, I like the expression you both put into the music, and Brahms is always a pleasure to listen to. Especially very good is your piano part. You could work as professional piano accompanist, if your technical profession would start to get boring. Along with your phenomenal sight reading ability, what is in so high demand as correpetitor and very few have this abilitiy!
I really tried to overlook the intonation problems of the viola, and I know that as piano player one has it so much easier regarding this. And I like also that earthy tone of the viola, everything, but it is always the intonation problem what impacts the pleasure of listening. Maybe the viola player could stand closer to you to hear better the piano?
I did not hear much wrong notes, and also the Upright sounds really good. The sound balance between viola and piano is ok, but of course it would be better to have separate mics to be able to mix it later with CoolEdit to have optimal sound balance and also stereo effect.