You’d be absolutely fine mate. Especially with having first dibs at the tickets, unlikely there’s going to be too much time pressure to select the seats either.
“Under 16s will only be allowed within the seated area and will not be permitted within the standing area.
Tickets within the seated area will be allocated at the time of booking and it is not possible to sit different bookings together.“
Reading that, sounds like you get what you’re given and can only get 2 together which is just
stupid if more than 2 of you qualify, especially when 2 are under 16