Drakensang Riddle of Rhymes

The first riddle mentions 3 swords and follow the hilt, then go as the crow flies past high obstacles and then understand something. The only thing I can think of is in the map, there's a small island with 3 trees together, which I believe is the '3 swords' in the riddle, but that's about it.

the graves of three soldiers

Did anybody do anything with the 'something' that shows in the crack by where the necromancer was? the dwarf noticed it, but I can't find a way to get there (mouse doesn't change over the thing either)

It's 5 arrows and schematics. Am i missing anything? wiki goes further about some kind of black tree on the stones, totem etc.
also found pretty rich stash on the skull island.

The grave of the 3 soldiers is the location mentioned in the first line of the first poem. That's the starting point of the search. The other place mentioned in the first poem is nearby. You have to interpret it line by line. The locations are marked on the map you linked to. The poems also include directions what you have to do, though. Some things are really hard to find, even if you know where to look.

It took just the right amount of time for me, 5 minutes or so, to think of the 3 buried mercenaries (sellswords) as the starting point. It then took me about 3 trips back and forth to that 4th grave before finally finding the additional message that was "barely legible". I was really feeling proud of myself, and had a tremendous sense of accomplishment in what was clearly turning out to be a challenging riddle.

Unfortunately, this hard-to-find clue was too hard to follow given the map and the non-descript terrain.

I, too, thought that an "island where many bones did rest" was Skull Island where I previously killed a mob of skeletons, and spent a good hour poring over that spot of land. The part that disappointed me was the part about "Lurking behind wood long dead, throned upon a black, black stone". The problem is, there were dead trees on top of black rocks ALL over the place in that marsh. I even found one in the starting village, right across the water from Skull Island, where you could clearly see a cluster of rocks (I was looking for "stony ornaments"). That's where I focused all my searching.

After an hour I finally gave up, searched the web, found the German wiki, and realized the point of reference was a completely different dead tree in what seemed like a random location. This pointed you towards the ruined temple and all the grave-markers (which I now figured must be made of stone). I really wish they had included some kind of unique landmark and referred to that, instead of simply a dead tree that could be found in various locations throughout the map. Or alternatively, they could have left off that label "Skull Island" from the map, as it created a needless red herring in this challenging riddle.

I'd like to think that I could have figured out the significance of putting together each half of the round gravemarkers to get to the right place, but I'll never know because I saw too many pictures online when I finally gave up and looked. Even though I got the reward, I felt like this was a failed quest that could have been great with just a tiny little different implementation.

I found the graves by the harpy hill I still can't figure it out.

Finding those trees from the riddle is not a big task, because they are all marked on the map. Finding the right one was difficult, though, because I don't think that any location really fit the description very well. Furthermore, the area was so dark on my computer that I didn't really recognize much that was further away.