Hi Lisa,
This is a tough problem, since having only 12 people restricts things a lot.
You didn't say exactly how many rounds you wanted to play, but I figured 6 might be about right, so here is my attempt at a schedule.
Table 1 Table 2 Wii
(C F v I K) (A D v G L) (B E H J)
(B D v I J) (C K v E G) (A F H L)
(A H v D K) (B E v I L) (C F G J)
(B G v F L) (C D v H J) (A E I K)
(A E v G J) (B H v F K) (C D I L)
(C E v H L) (A I v F J) (B D G K)
Players play twice at each table and twice on the Wii. When playing Euchre each player will have 4 different partners, the 8 opponents however will not all be different, so it's possible that schedules with better opponent balance do exist.