Thank you to all of you for making this possible!!
About Virtual Choir procedures:
Using Soundtrap is completely optional. It can be helpful for rehearsing while hearing other parts (if others have added their tracks) and with the piano track. But there are no visible cues, so length of fermatas, retards, etc. have to be guessed. So feel free to:
Use it as a tool, just for practicing your part.
Use it to record your part, using headphones. Also send a separate video (no need to wear headphones - pretty much lip-synching).
You could also, instead, send a video with audio, using headphones and watching the conducting video (I will extract the audio and mix it with all other audio tracks). Remember to use the landscape setting on your phone.
OR you could send an audio file (even recorded on your phone or computer, just not caring about the image) as well as a video file where you focus only on the video part (and you don't wear headphones) - also watching the conducting video.