Question: At the briefing it's pointed out that there's a hospital, school, etc. around the factory they're bombing, and Dennis is very adamant about getting the bombs "right in the pickle barrel" so a lot of innocent people don't get hurt. But the planes are spread out over a large area in the sky, and are also moving when the bombs are dropped, so wouldn't the bombs land over a large area and not just in the limited vicinity of the factory?
Answer: Even with the Norden bomb sight, during WW2 bombing was generally very inaccurate.
Question: What was the ball of fire as the planes are landing to the right of the screen?
Answer: That would be a flare being fired from the aircraft. Yellow ones meant the aircraft had sustained serious damage, although that was often self-evident, and a red one meant that there was a seriously injured crewman on board - prompting first aid teams to be ready to meet the aircraft once it had landed. Their was also an unofficial green flare that meant someone had completed their tour of duty.
Chosen answer: It would seem that every plane's Norden bombsight would drop from different angles, etc., each designated for a common target. So, 2 planes could be higher, lower, ahead or behind the target and each hit the target, if the bombadiers had an accurate fix on the target.