Almost. Codeshare exclusively refers to an arrangement where the operating carrier is different than the marketing carrier -- e.x., UA8001 (SEA-NRT), operated by ANA. You cannot apply an upgrade instrument to a codeshare flight. It has to be converted to the native flight number -- in this case, it would be NH177 -- in order to apply an upgrade instrument. That is, the flight number needs to be updated and then the ticket has to be reissued. In other words, UA8001 is ineligible for upgrade, but NH177 is eligible (assuming you have a high enough fare class). The reason is a little opaque, but basically you can think of it this way: codesharing is an agreement where one airline allows another to sell some of its seats under its own code, but that agreement doesn't extend to award / upgrade seats. Therefore, you can't waitlist for an upgrade on a codeshare.
Award tickets are never codeshares. It sounds like what you have is either (a) an interline ticket, UA connecting to TK, or a (b) a TK-only ticket paid for with MileagePlus miles. In either case, the reason that you have two PNRs is that each operating airline, plus the ticketing airline, stores the information that's relevant to it into its own Computer Reservation System (CRS), creating a Passenger Name Record (PNR). The ticketing airline needs the entire itinerary, because it has to ensure the the electronic ticket matches the itinerary that was created. Each operating airline only needs to know its own flights, plus the single flight connecting to it, and all flights downline in case they have irregular operations (IRROPS) and need to, e.g., reroute the passenger. Therefore, every ticket you buy from United will always be entered into a UA PNR. Your transaction may also result in the creation of one or more Other Airline (OAL) PNRs, if your itinerary includes non-UA airlines.
This is orthogonal to the issue of converting a codeshare. In the example for this thread, where OP is flying LH but has booked the UA codeshare for that flight, it was inevitable that both LH and UA would have PNRs to store their information for that record.
If this seems overly complicated -- it goes back more than 50 years, to the era of paper tickets. At one time, the reservation only included the itinerary information, and the ticket was a separate book of paper coupons that the passenger had to carry with them and exchange during the boarding process. Although it's a lot more integrated now, there are still remnants of the old system if you know where to look.
Happy to help.
We were all beginners once.