Does "If the total cards in both players' security stacks is 6 or less" mean 6 or less cards in either me or my opponent's security stacks?
No, it means if the total sum of cards in your security stack and the cards in your opponent's security stack is 6 or less.
Mar. 28, 2024
If this card is revealed from my security stack and trashed by [BT10-086 Omnimon (X Antibody)]'s effect, does this card's “When this card is trashed from a security stack by an effect” effect activate?
No, it doesn't. A card revealed from your security stack and then trashed isn't considered "When this card is trashed from a security stack."
Mar. 28, 2024