Kaya, Ghost Assassin is put in play, I'm the AP and I have a card with keyword 'dredge' in the yard. I [-2] Kaya, who signals intent first?

Opponent will definitely submit a card face-down as the discard, but are they doing this before or after I signal draw vs dredge? Or do I get perfect information, and choose whether or not to replace draw after their discard is turned face-up? The poor formatting on this card using the word "and" [you draw a card] versus "then" [you draw a card] or doing something like "each opponent discards. draw a card." I think the current formatting means this is simultaneous, except we also have a replacement effect going on...so maybe this is an AP/NAP order thing. It's quite odd.