Did griffin know about the beleith's activation?
You're thinking of chapter 72-73 of the manga, if you want to look it up (Volume 12).

Griffith sits in the lake, picks up the Behelit and remembers what Zodd and Wyald told him. "Use it. Call them. Our guardian angels!". As the solar eclipse happens, he most definitely realizes.

He then crawls backwards, away from the rest of the Band, hoping to not draw them Edit: Guts into the eclipse.

On the matter of sequels, the actual series has no second season. There are the 2013 movies (Berserk: The Golden Age) or the 2016 series ("Berserk 2016").