When you’re adding a real choir to your music, in most cases it is recorded seperate from (and after) the orchestra has been recorded. There are three main reasons for this:
A choir needs to rehearse and can’t really sing music prima vista. Even the best choirs need to sing through passages several times to get it right. Orchestras however are quicker on sight reading and therefore you will lose a lot of time and money rehearsing passages with the choir while the orchestra is sitting idle in the room.
The second reason is, that unless you have a massive choir, it easily gets overpowered by the orchestra playing the “epic film music style” and is very hard to recover properly in the mix later which is easier when recorded separately.
Also only the largest recording venues (like Abbey Road) have the space to incorporate a big orchestra and choir at the same time. Most studios are laid out to only provide enough room for one of each.