Why is the influence of the Druchii in a necromancer's work in Sylvania. Does necromancy have some kind of ancestry from the dark elves?
Yes. Nagash tortured the secrets of Dhar out of some Druchii, and used that as the basis for necromancy.
Vanhel is the guy whose diary we read, right? Why do elven Grey Lords know about him? I mean, I guess he's famous enough they would have heard about him, but they talk like he's a guy whose career they followed with interest or something. They were alive when Vanhel was alive, right?
Frederick Van hal was a Baron of Slyvania when a bunch of really bad stuff was going on - plague, warpstone meteor shower, and then Skaven drawn by the warpstone. To fight back against the Skaven invasion Van Hal accepted assistance from a fellow called Vladimir von Carstein, a vampire who taught him necromancy (keep in mind that this was back when both vampires and necromancy were unknown in the Empire). This turned out pretty well in that he actually fought the Skaven to a standstill, but the downside was that it also drove him insane, and Vladimir mercy-killed him.
It might be that they're talking about him as if they're intamtely familiar with his work because the Eonir allied with the
Emperor Mandred Skavenslayer during the Skaven wars. Vanhal was on the other side of the Empire from their forest, but it's pretty likely that they heard about his exploits as they were pretty relevant to the war with the Skaven. And yes, both Grey Lords are definitely old enough to have been alive back then.
I don't know what point he was making here, I don't know what a Widowmaker is, and I don't know who Yngra is.
The Sword of Khaine - also known as Widowmaker, and by a bunch of other names - is a stupendously powerful weapon, which was used by
Aenarion the Defender - first phoneix king of the High Elves - to fight back against a massive Chaos invasion. This worked pretty well in that he actually beat the invading armies, but the Sword of Khaine also turns people into homicidal lunatics. Fortunately(?) Aenarion died to his wounds shortly after drawing Widowmaker so he didn't get to go on any murder sprees, but his blood line is cursed by it to this day.
Seilph is comparing necromancy to Widowmaker, in that both are powerful tools that
will cost their users their sanity but
could be used to good ends, and in fact
were used so to dramatic effect in the past. The point he seems to be making here is that there's a sense in which those tools are 'honest'; war
always takes a toll on the sanity and morality of those that participate in it, so maybe it's better that those tools tell you their cost up front.
Yngra is another Grey Lord. They were briefly mentioned before, they worked on the Waystone foundation IIRC but we don't know much about them. Presumably they wouldn't approve of what Seilph is saying here, which isn't surprising as this is a pretty spicy take.
I remember that Vladimir was the guy who taught Vanhel necromancy, and I think he tried to become emperor. Who were Konrad and Mannfred again? All I can recall of Mannfred is that he was the Emperor known as the Skavenslayer, and that's probably a different Mannfred right?
Vladimir is the vampire responsible for Sylvania being Like That, Konard and Mannfred are two of his heirs, vampires he turned personally. Each is responsible for starting one of the so-called
Vampire wars. Vladimir used dark magic and tried to take over the Empire but was arguably an ok ruler if you don't mind paying your taxes in blood, but Konrad and Mannfred were giant assholes with pretty much no redeeming features.
Who is Aenarion, and what is Heavenblight, and in general what is Seilph talking about here? Does Mathilde know who this person is?
Then I think I basically understood the Norscan discussion.
Aenarion I mentioned before. Heavenblight is one of the many names of Widowmaker. According to legend, after using Widowmaker Aenarion regained his sanity long enough to take it back to the Shrine of Khaine before dying of his wounds, and since then it hasn't been drawn. This is why Seilph says "we only had one" - there hasn't been anoter wielder of Widowmaker since Aenarion just like there hasn't been another necromancer of Van Hal's caliber in the Empire (this is kind of a tenuouspoint to make because there've been plenty of necromancers since, but I suppose Seilph thinks they don't count because they didn't try to use necromancy for the greater good).
Seilph seems to say that the story of Aenarion giving up Widowmaker is more myth than fact, and that's part of why no one wants to use it: if the question of what happened was settled either way, if you know for certain if you can put down that terrible tool after using it or if you'll be consumed by it, then maybe someone else would be willing to use it (either because they know that it's
possible to relinquish it once you're done, or because they know it's
not and so they know the price they'll have to pay? I don't think Seilph is making a great point here tbh but I think that's the point he's making).
I thought dhar was considered legit for elven archmages to use, even if they don't use a lot of it. Is it actually considered not legit for them to use, and their own people (I assume the Ghost Striders) will punish them for it? Who are the Ghost Striders?
Ghost Striders are Eonir commandos who apparently hunt out Chaos users. I think 'The Other Path' Sarumar is talking about there is Chaos, or maybe evil in general. I think it's not a point about Dhar specifically, but about the corrupting nature of using evil means: even if you don't get taken down by Elf Police or Ulrican Templars, you're still going to lose your metaporhical and/or literal soul so it's probably not worth it.