I don't think that a cracked injector in #4 would flood out #2, so it probably wouldn't be a bad idea to replace them both.
In fact, if you have the money, it probably wouldn't be a bad idea to replace all four injectors just in case #1 & 3 let loose later.
If the injectors were leaking fuel into the cylinders, its possible that those two cylinder could be washed out. That means they may have no compression, so you'll have to squirt a little bit of oil in those cylinders to get the compression to come back up while cranking the engine with the plugs removed, all injector connectors unplugged, and coil unplugged.
You don't want gas or spark going on while your trying to restore compression while cranking the engine.