Hi, newbie here. Got some questions regarding advanced seat selection on my rtw flight.

The ticket was booked through a travel agent and ticketed by Air New Zealand. In total four carriers are used: SQ, LH, UA, and NZ. The booking can be retrieved in all airlines' website except for NZ...weird.

SQ does not offer any seat selection at the moment. I don't know why. On UA site, I can only select seats on United flights, and UA charges extra for E+ seats. While on LH website, I can select seats for three airlines except for NZ. On LH's site, the availability of SQ seats is very limited, considering the actual travel date is 6 months later. And interestingly, E+ seats of United flights are free on LH page.

So I am wondering, where will I be able to select NZ seats? Why United E+ seats are free on LH's website but costs extra on their own page? And if you select different seats on United flights through UA's website and LH's website, which one will override the other one?

Hopefully my description is not too confusing... Thanks.