I can say on the basis of theory that no 'nice' schedule will be possible for your 12 player scenario, I don't have any software that can try to make such a schedule, but I am sure the balance would be very poor. However, I can offer something for 16 players (6 women and 10 men) and 5 rounds - this can work well with every player being scheduled to play with every other player exactly once. I have labelled the female players F1 to F6 and the male players M1 to M9 plus MX for the tenth man.
Court 1 Mixed Court 2 Mixed Court 3 Mixed Court 4 Men Only
(M4 F1 v M6 F2) (MX F6 v M9 F3) (M7 F4 v M8 F5) (M1 M2 v M3 M5)
(M9 F5 v M5 F2) (M4 F4 v M2 F3) (M1 F1 v M7 F6) (M6 M3 v M8 MX)
(M8 F6 v M2 F2) (M9 F1 v M3 F4) (M6 F3 v M1 F5) (M5 M7 v M4 MX)
(MX F1 v M2 F5) (M5 F6 v M6 F4) (M3 F3 v M7 F2) (M4 M8 v M9 M1)
(M1 F2 v MX F4) (M3 F5 v M4 F6) (M5 F1 v M8 F3) (M2 M6 v M7 M9)
Each woman has 5 rounds of mixed doubles, playing with all ten men exactly once (5 as partners and 5 as opponents), and opposes each other woman exactly once.
Each man has 3 rounds of mixed doubles, playing with all 6 women (3 as partners and 3 as opponents), and has 2 rounds of mens doubles.
Hope that is of some help.