Not quite sure what you’re aiming for here, but generally speaking, it’s difficult to “phatten up” a basic sound without it sounding synthetic… And I suppose you’d want a choir to sound big and organic?
In this case, if you want to make it sound like a bigger choir, you’re not going to get great results from any normal chorus effects, as they tend to basically just be modulated delay lines, always giving some amount of that characteristic flanger/phaser quality side effect.
Might want to layer multiple instances of the sound, so you can process them individually. You can edit the SoundFonts and/or or offset and automate the tracks to get the instances “out of phase,” so it’s not literally a few instances of the exact same sample playing synchronously, as that would produce the same result as a basic chorus effect.
Basically, the closer you get to just throwing the samples in a synth/sampler and editing away, the greater the possibilities of creating a much bigger and/or totally different result. The really interesting stuff going on in synths and samplers is usually much more involved than just applying effects to a steady audio stream.