Which series in the Heroes Chronicles did you like the most?

No, in Enroth, it's original. In general, the Heroes games are mostly an apocrypha in relation to the Might and Magic universe.

Added 2 minutes later
No one touched Sandro from Xeen. The presence of a character named Sandro is a mistake by 3DO in the Heroes games (they developed them separately from NWC, and this is what happened). Sandro from Xeen's fate is unknown after the end of Might and Magic V (probably, making him alive again meant he was still alive). Sandro, a student of Etric the Mad, led the Necromancer Guild of Jadama, and when the Reckoning occurred, he moved to Axoth.