I think:
As person B accelerates to nearly c, he will warp space time a ridiculous amount. This means he will exert a lot of gravitational force on his surroundings, and also he will perceive time in his surroundings moving alot faster, as well as his surroundings perceiving him moving slower. so it will seem to person B, that person C is moving alot faster than he actually is. I haven't worked it out, but I believe that person A will still see person B moving faster, as he is running STUPIDLY faster. you also have to take into account the fact that person C is on the race track with person B, so he will be in an area of space-time that is significantly warped too. Also im not sure, but i think having the mass of a person going at 0.999c will probably cause i black hole.
im not an experienced physicist tho so im not sure