Air NZ / UA flights - 1 ticket. Can I buy E+ on UA later?

[Vacation1]

Hi.
Not sure if this is the right forum for this question.

For SYD to IAD all booked on one ticket through Air NZ website.

ANZ PE to the US via NZ and then UA Economy for the domestic flights to and from East coast of the US.

If I do a dummy booking I can choose seats in PE on ANZ but get the message that I cannot select seats on UA, only give a preference for aisle or window.

Here's my question(s):
Will I be able to access my UA booking once I get the Air NZ PNR in order to purchase E+ seats on the UA flights?
Will I get 2 PNRs at the time of booking - 1 for ANZ and 1 for UA?
If no, could I buy E+ seats direct through a United call centre?

I'm a member of both airlines' mileage programs if it makes a difference but no status at all.

Thanks

 

[kyanar]

If you sign into United.com, under "Find a reservation by confirmation number" enter in your Air NZ booking reference and surname. The system will pull up the entire itinerary with the United confirmation number, and allow you to seat select for the United sectors of the flight.

You only see flight legs which contain a UA operated sector (i.e. if a return flight and no domestic sector on the return leg, it will appear as a one way)

 

[Vacation1]

Thanks for the info.