... and since Dragon has no airlock, they will either:

(1) have to add one, (2) have actual EVA suits for all crew memebers or (3) keep the rest of the crew in their flightsuits in the vacuum inside the capsule while the hatch is open during the EVA.

If I had to guess, I would think that it is (3). This way they wouldn't have to carry a flightsuit and EVA suit for each of the crew members. The suits of the other crew members would still be connected to the capsule which takes the role of the environmental control and life support system.