According to the plot of this map, are Sandro from Xynda and Sandro from Enroth the same lich?

It seems the creators of the fan-made lore decided that they are the same. I share this opinion.

Enroth, according to this map, was colonized about ten thousand years ago (the sign near the sulfur mines)?

Yes, approximately 10,000 years before the Great Silence.

Where are the County of Douglas and the Edge of the World located geographically? Not far from Varna's Tomb?

No, of course not. Somewhere very far to the southeast of Enroth. I can't be more precise; "The Edge of the World is not a place, but a state of mind." I don't think it's worth seriously connecting it to Enroth. You and I have several opinions about what it is, ranging from the aforementioned geographical location to a parallel universe, or some kind of "Bottom of Worlds" that can only be reached if you search for it very hard (and unconsciously).

Thank you for your feedback. I'll fix the bug tomorrow and upload the finished version.

P.S. How are the 777 Archangels? Are they killable? I looked at what kind of maps people are making here and seriously doubted my own criteria for "manchikinism."