Bang's 5A is a level 1 move with 11 frames of blockstun. Bang's 5B has 10 frames of start-up. So there is a 2 frame gap in 5A > 5B on IB. It doesn't matter when he cancels it since blockstun starts from when you block it and the fastest 5B can come out after you block 5A is 10 frames.
Both hits of Mu's 6B are level 4 (18 frames of blockstun) and with a 9 frame gap between them, you can't doing anything.