if I play 2 Deadbloom Predators to the same occupied BF revealed by 2 Dazzling Auroras, do they both participate in the same showdown or do they enter 2 separate showdowns?

One showdown. Both Deadbloom Predators are controlled by you at the same enemy battlefield, so only one Contested status exists there — that battlefield stages a single Showdown/Combat, and both Deadblooms fight together in it (FAQ #1207; CR 323.7–323.8).

Here's the sequence: Aurora #1 resolves and plays the first Deadbloom, staging the showdown but not starting it. Aurora #2 resolves, and since the battlefield is still enemy-occupied and not yet in combat, the second Deadbloom is a legal play to the same battlefield. Once the chain empties and cleanup runs, the one staged Combat opens as a single Combat Showdown where you're the Attacker and both Predators participate together (CR 344, 466.2.c).