You should be able to get two seats in the Select Seating zone, even if your companion has no status, they have to be in the same booking and a better trained agent should do that.
If the european flight is operated by KL Cityhopper, I doubt, that there is a seperate boarding call or a seperate KL/NW line at TXL, but I never was to TXL on KL...
KL Cityhopper planes have one class configurations...
If it is a Fokker 70, try to get seats in row 1 or 11.