Ugh, I'm sorry to hear your guys' recoveries haven't gone smoothly. I suffered a bilateral exactly 1 year and 4 days from today. I was back on the tennis court at 6 months (albeit moving slowly!) and I've been doing 10 mile bike rides and 3 miles runs for the last couple months without much hassle. I was 32 when I suffered the injuries and overweight (5-8 and 225lbs) but I have an extremely athletic background luckily and something in me snapped other then the tendons and I have completely invested myself in weight loss, rehab and learning every single thing possible about this injury with a vigor that surprised me and certainly my surgeon.
My right knee gives me almost zero trouble at all and most days it feels like it never had the rupture during everyday walking around. The left knee gives me some trouble from time to time especially after a hard day at the gym but it's nothing a little ice and rest don't clear up.
I say this stuff not to brag but just to give you guys some optimism that if you work hard and continue to rehab you will get better.
Many of the problems you are experiencing with stairs and hills and overall weakness are due to weakness in a specific area of your quad -- the VMO. This area atrophies rapidly after the injury and you must target it in rehab in order to rebuild it. I do two specific exercises for it:
I highly encourage you to incorporate these into your rehab, at least a couple of them:
http://sportskneetherapy.com/the-best-vmo-exercises/I also recommend doing eccentric style training and plyometrics.
https://www.youtube.com/watch?v=aBqRrxxKoisYou also might want to invest in a slide board in addition to a slant board. You can buy foam slant boards on Amazon for $15. Slide boards are a bit more pricey but some gyms have them.
As far as supplements I encourage you to take creatine and cissus. Cissus is magic for the joints IMO.
I also encourage you to foam roll as much as possible and to use a gua sha scraping tool once a week on the knee. You can google the technique but basically you just "scrape" downwards along the patella this helps break up the scar tissue.
Cold plunges also work wonders for inflammation and alternating hot and ice therapy is great as well.
I wish you guys the best remember to push yourself but if you feel pain more than a 4 on the scale back off. But, you will experience normal pain when you are doing these exercises especially the eccentric squats. Just know that eventually it will lessen as you strengthen not only the leg muscles but also the tendons themselves.