This question is about Curse of Strahd. It is essentially a completely-spoiler question, so, if you plan to run it (as a player) and you do not want to get spoilers, avoid reading this question or the answers. I will still try to use the spoiler block when appropriate, but keep in mind some things might slip.
So, if we check p. 6, in the Introduction of Curse of Strahd, it states that the Old Bonegrinder is a 4th level area. However, that area contains
Three Night Hags, each one being CR 7 (as they are in a coven), as well as possibly Nine Dretches that Morgantha can summon.
This makes me confused about what is the point of this area. My assumption is that the characters are supposed to
rescue the two children (or three – if they didn't stop Lucian from being kidnapped, I guess) and stop the operation of the windmill
but I doubt the monsters in the area will let them do that without a fight. They can try a stealthy approach to accomplish the goal I mentioned, but that's very dicey – failing a Stealth roll might be deadly here.
Even if they manage to split the monsters, that still may be a deadly encounter.
So, essentially, what I am asking is: what is the goal of this area and how is that appropriate for 4th level characters? Alternatively: Am I missing something that makes this way easier than I am thinking and doesn't lead to a TPK in half of the possible scenarios?
Note: Yes, I do understand that they could just approach the Windmill, see the Raven, listen to its advice and turn away. What I am asking is: what is the actual goal of the area that is supposedly appropriate for 4th level? I don't think taking a look in the windmill and turning their backs is exactly a goal (or running away after Morgantha tells them to.)