There are two ways to interpret that sentence, and it hinges on a weirdness of how English uses the indefinite article.

Any character or monster that doesn’t notice a threat is surprised at the start of the counter.

The usual interpretation of "a threat" here is that it means "one threat". If that is the correct reading, your question is the result. Is it correct though? This meaning would require that surprise is a relationship between two individuals, so that the dire wolf could be surprised by the rogue but also not surprised by the enchanter.

Is this how surprise works? It turns out, no:

If you're surprised, you can't move or take an action on your first turn of the combat, and you can't take a reaction until that turn ends. (PBRv0.2, p. 69)

Surprise is not a relationship between two entities, it is a state of a single entity. It's impossible to be surprised by one opponent but not surprised by another.

Is there another way to read that sentence about "a threat" that makes surprise sensible as a state? As it turns out, yes.

"English is funny that way"

Another use for the indefinite article, which looks identical to the "one threat" meaning, makes the sentence in question

Any character or monster that doesn’t notice a threat is surprised at the start of the counter.

mean any threat at all, not just one. If this meaning of "a threat" is how it's being used, then that means only creatures who notice no threat are surprised.

Because this reading is perfectly normal English, but ambiguous, we need to confirm the reason by looking for clues in the surrounding text. That confirmation is in the definition of surprise we looked at above: being surprised means being completely surprised, which only makes sense if it happens when no threat is noticed.

So the dire wolf is not surprised, because it did notice a threat, as opposed to not noticing a threat. (See how that makes sense put that way?)

On the plus side, the champion and the rogue don't need surprise to have advantage on the dire wolf, because that doesn't rely on surprise, but rather on being unseen, and being unseen is a directional relationship, not a state.

If you read the following paragraph in the PHB after the section you mentioned on turn order (pg. 189) you'll see it says:

If you’re surprised, you can’t move or take an action on your first turn of the combat, and you can’t take a reaction until that turn ends.

On top of that, it's important to note that

A round represents about 6 seconds in the game world. (PHB 189)

So in this case it translates to:

1. Warrior takes his turn. He can choose to ready an action here to use his reaction later to attack Elf2 when the Rogue attacks Elf1. Note that the Warrior can move into range if necessary and will not affect surprise as surprise is determined before turns are taken.
2. Elf2 does nothing and is no longer surprised. He can now take reactions. If the rogue attacks him there are no bonuses related to surprise added to that attack.
3. Rogue takes his turn. When the Rogue attacks Elf1, the Warrior uses his readied action.
4. Elf1 does nothing and is no longer surprised. He can now take reactions.
5. Combat proceeds as normal using the same initiative order. (Readying an action does not change initiative order so it will still be Warrior, Elf2, Rogue, then Elf1)