2: As I reiterated, value is a mental object, murder is a non-mental object being arbitrarily correlated with value. So when someone values murder, it just means murder is one of the things that triggers value for them. So "I value murder" means murder creates value for the speaker, as "that hurts" means "that" creates pain for the speaker. So value existing in one person's mind will never be able to contradict another person's value. Again paralleling perfectly with pain and any other mental object.
A relative proposition can still be inherently true. "X is cold" does not mean placing X in all circumstances, it must remain cold. It just means X is cold there and then.
"I like purple" is just another relative proposition. It has a location (I) and a time (when the statement is made). It just means that person values purple there and then.
If relative propositions aren't "inherently true" then I'd have to ask what the point of that definition is to the topic? It would mean values exist in certain locations, and are found valuable (are valuable in certain locations), which is not nihilism in any sense. I certainly didn't get the impression that that was the definition Heisman intended.
The bolded is exactly what I thought he was saying. He's not denying their existence but claiming they aren't important (have no merit) and strangely dismissing their existence as irrelevant. Rather like he doesn't value them.