Recently flew Condor Airlines for the first time from SEA to FRA with a Lufthansa code share from FRA to Basel, Switzerland (BSL). Our trip home took us from BSL to FRA, again on Lufthansa, then from FRA to SFO on Condor and the final leg was SFO to PAE in Everett on Alaska/Horizon.
As mentioned in previous Condor posts they only allowed printed Condor boarding passes from the airport at SeaTac, nothing printed at home, from another airlines OR even their app. The app might have worked in Frankfurt but I didn't try it.
The Condor website was a bit confusing and it sounded like you needed to check-in with each airline on your reservation separately but that turned out not to be the case. Your initial check-in covered all of the flights. Our checked luggage was also booked through to our final destinations. I didn't reach out to Lufthansa or Alaska to pick seats so for the first Lufthansa flight my wife and I were not seated with each other.
My big tip, which is actually more of a warning, is that you REALLY SHOULD CHECK-IN as soon as you get the email from your first carrier. I got the email from Lufthansa but since they usually need to check your passport anyway I figured I would just do it at the airport. Come to find out from the lady behind the counter because we had not checked-in online we had been moved to STANDBY for our flight. Needless to say that's not the kind of thing you want to hear at 04:30am. Thankfully we made the flight but I'd like to save someone the unneeded stress.