I finally found a way to complete stage 9-5 and 11-5 on nightmare with two champions. The only problem is, when i complete the stage, i'm only rewarded 2 stars instead of 3. Would be great to receive the sacred shard during the double change weekend.

I am using martyr and Reinbeast and they both are alive at the end of the battle. 

And no, Martyr does net not get revived by Reinbeast.