Affection = How much they like each other.
Affinity = How well they agree with each other on moral dilemmas.

So Affection is something like measure of personal relationship and Affinity is something like measure of confidence.

But:

1) Is possible to reach negative values and is there any maximum? (-100 , +100)

2) We have these values for each companion, or only for two main heroes?

3) Is possible to outsmart the views of companion/second hero?
For example:

Companion: You are killing shaggy bunnies! You are evil! (-1 Affection and Affinity)
Hero: (persuasion) These are not shaggy bunnies, these are... demons! Yes, demons!
Companion: (persuasion successful) Really? In this case, we have to kill them all! (+2 Affection and Affinity)

Love your example.

In the beta I got both my character to level three and I check their 'stats', or whatever they are. Honestly I couldn't make heads or tails of them and I really couldn't tell how I got those scores. The two basically had the opposite colors, one had blue bars, the others red, etc., but I always had them to end up agreeing with each other. In fact with their general discussions they generally fully agreed without every having to play the rock/paper/scissors game.