QWhen playing this spell, if I have exactly 10 cards in my cemetery, including a Rulenye, Omen of Silence, will each opponent still have to discard a card after I summon that Rulenye, Omen of Silence from my cemetery?

AYes. Necrocharge references the number of cards in your cemetery at the moment this spell begins to be resolved, so even if the number of cards in your cemetery drops to 9 after summoning a Rulenye, Omen of Silence, you would meet the requirements for "Necrocharge (10)."

QIf I have at least 10 cards in my cemetery, but I don't have a Rulenye, Omen of Silence in my cemetery, can I still play this spell?

ANo, you can't.