I have seen two quite different examples of ensembles from home recently.
Sadly, the obvious solution of a web conference is unlikely to work as even good internet connections will probably have too much lag and feedback could be an issue.
One is Gareth Malone's Choir at Home. I have been following this and the procedure is explained. You download a guide track and listen to it on headphones while singing and recording yourself. Later, the recordings will be assembled. We have not heard the result yet.
Here is a rather different example: The Rotterdam Philharmonic at home. This time the procedure is not explained.
How might it be done? I am not asking how the Rotterdam Philharmonic did it specifically but just how this could be done, especially techniques that relative amateurs could use.
I guess that each player could listen to the same recording of the piece and play along with it. The need for someone with the skills to collect the results and mix them seems unavoidable.