Aren't you missing 'duet'?
There are times I like to listen to a duet.
Usually male/female, sometimes classical, sometimes modern (pop).
If 'vocals' is a defining factor here, 'type of artist' could be a little bit vague and ambiguous?
Perhaps simply 'vocals' would be better?
Male, female, tenor, soprano, countertenor, duet, choir, spoken word, etc.?
edit:
Since we are in the 'General' board:
A freebee jewel, classical female/female duet:
https://www.youtube.com/watch?v=C1ZL5AxmK_A