It might also be that Crows do not recognize the hobbits as at threat to report? Hobbits are less known outside of their own realm and maybe the crows thought of them as just another wild animal?
It's too late for that argument by that point. Sauron (and Saruman) are aware of hobbits and that one of them has the ring -- hence the Nazgul showing up in the Shire even before Frodo gets on the road.
Yes, but you're assuming information flows flawlessly. Crows are pretty cantankerous and mischievous at times. I wonder how hard it would be to get them to sit and listen to descriptions of Hobbits. Also, maybe all humanoids look alike to them?
