Welcome to EK Sarah.
I suppose you mean Emirates?
On the Dublin-Dubai leg you will have a A330-200( Unless you are travelling post 28 Oct), a very old aircraft( In EK terms).
This aircraft has PTV but not on-demand.
If you are travelling as a pair I would recommend a window seat pair.
A seat map can be found here-
Seat Guru
On the next leg to Sydney I would assume you are on EK 414, but correct me if Im wrong.
This will be on a 777-300ER, and features a very good Entertainment system, Emirates' ICE.
These aircraft have 3-4-3 configuration so if travelling together you may either want to take two seats in the middle or try for the back 3 rows which have her seats, but these have some disadvantages. Another expert may be able to tell you how full your flight will be and if it is poorly booked you may want to choose one of the window rows at the back and hope no one else is there.
A seat map is here-
77W
Happy New Year and enjoy Australia.