Odd foul situation

[Adam]

I don't think it matters. The only thing that might matter is whether B2 gained LGP before A1 last left his feet prior to contact between those two.
If the act of shooting has begun, the shooter can become airborne even after the foul, and then he is protected until he lands. So, you could have the following order of events:
1. Shooting motion begins by A1.
2. B1 fouls A1 from behind.
3. A1 jumps off his last foot for the layup he began before the foul.
4. A1 crashes into B2, creating a block/charge situation that could be called based on whether B2 gained position prior to A1's takeoff.