Hi @wawoodman, you can copy the S and A and then use (selecting the destination rest on the upper staff of your Choir reduction instrument) and then mouse right click) Paste Special/Reduce, and do the same for T and B.
Dorico will take care of the voices assignments automatically:
To handle the lyrics, make sure first that the lyrics of S and T are Above the staff (select S and T, filter for Lyrics and press F), and they will maintain this property, when Reducing:
To make the editing more comfortable I suggest to work in Galley view, and expand the Ideal Staff Gaps for Galley view to something like 180% (this just make the fixed distance of staves in Galley view bigger, and doesn’t influence the spacing of Page view. When you go back to Page view all the spacing are adjusted automatically accordingly to your Layout Options etc.):
