This problem can be solved by first starting with a standard round robin schedule for 12 players. Split this into two equal parts to represent the two venues, next remove two of the rounds, and finally add back the removed matches as the 4th match at carefully chosen venues. To get the schedule below I have started with a court balanced round robin and have made sure that the 4th matches have been added back to the same half of the schedule that they originally came from, this ensures venue balance where teams play 5 times at one venue and six times at the other.
Venue 1 Venue 2
(C F) (H L) (I K) (C L) (D E) (A J) (B G) (E J)
(G K) (A I) (H J) (A G) (F L) (C D) (B E)
(A H) (F J) (G I) (F H) (E K) (B C) (D L) (C K)
(G L) (C E) (B F) (A D) (I J) (H K) (D J)
(E F) (B I) (J L) (E I) (C H) (D G) (A K) (G H)
(B D) (A C) (E L) (A B) (F K) (H I) (G J)
(D I) (B K) (C J) (D K) (A L) (F G) (E H)
(B J) (E G) (D H) (C I) (A F) (K L) (F I)
(J K) (D F) (C G) (B H) (I L) (A E) (B L)
Hope that helps.
Ian.