Step 1: Understanding the Correct Preposition
The correct preposition is "round" because it is commonly used when referring to sitting or gathering around an object, such as a table. This preposition implies that people are positioned in a circular or surrounding manner relative to the table.
Step 2: Evaluating the Other Options
- "With" would suggest sitting next to or together with someone, but it does not fit the context of describing a position around an object.
- "After" is typically used to describe a sequence of actions or time, which is not relevant to the physical positioning in this context.
- "Till" refers to time and does not apply in this situation where positioning is being described.
Step 3: Conclusion
Thus, the correct sentence is: "They were all sitting round the table."