Same with miles, its one 'upgrade' per fare component in a direction. So as you mentioned if that outgoing with stopover is on the same fare basis and it allows a stopover, it would only require 1 15K mile upgrade per person.

Not sure if this is the best place to post, but I'm wondering if anyone knows of a way to search for O-class availability on KL. EF only shows availability for Flex awards, and I think O corresponds to a Classic KL award.

I'm trying to book a SFO-AMS-SFO trip and upgrade using miles, and the easiest routing is KL on their direct. But of course, DL isn't showing any availability for O, so if I wanted to book right now and upgrade I would have to book a Y-fare. DL routing isn't doing any better either.

Also, it seems like if the flight is on KL metal, the following fare and booking classes are needed:
M -> not eligible
B -> O
Y -> Z

Not completely free. You start with 200 free "points", and get 100 "points" every 90 days added. Every time you search it costs points and more complex the search the more points it costs. Once you have used your 100 points you have to subscribe to use it.

The 100 pts is probably enough if you are a casual user, but if you do an automated email notification (only daily option available) you can use them up on one search easily before 30 days (4 points is my average search).