[ignore this, I think I'm wrong]
Yes #1 can shove over #2, but things get a little funky. The reason #1 can shove over #2 is because #2's all in *is* a raise...he called you for 20 plus raised you 4.
However, anything #1 shoved in for over 4 (#1 only raised 4 more than the last bet) is put into what's called a "side pot". Anymore additional money you put in gets put into the side pot, and if #3 calls, then 4 of his chips go into the main pot and the rest into the side pot.
Now, if #1 or #3 wins then they get ALL the chips. However, if #2 wins, then he gets everything in the main pot and the side pot goes to whoever came in 2nd place.
So for example, lets say:
#1 bets 20, #2 shoves 24, #3 calls 24
At this point, the pot is 68.
If #1 shoves, then the main pot becomes 72 (68+4), and the side pot become 96 (100-4). If #3 folds, then the most #2 can win is 72. If player #3 calls, then the most #2 can win is 76 (72 + 4 from #3).
4 comes from the fact that #2's raise was only 4 more than yours.
Let us know if you have questions, because theres a lot of number being thrown around in the example lol