When you have a complex itinerary and are not familiar with the basics, it is a lot better and easier to pick up the phone and call the original operating carrier, in this case LH. You will pay a phone booking fee, but in the end you will have the certainty of a properly ticketed itinerary.

Alternatively, go to an experienced local TA used by friends and colleagues (not an online operation) and explain what you need. Again, you may pay a fee for this service.