It may be helpful to your audience to move these parts of the story about Stephen together by using a verse bridge as the UDB does. (See: [[rc://en/ta/man/jit/translate-versebridge]])
This part of verse 1 is background information about the persecution that began after Stephen's death. This explains why Saul was persecuting the believers in verse 3. (See: [[rc://en/ta/man/jit/writing-background]])
The word "all" is a generalization to express that a large number of the believers left Jerusalem because of the persecution. (See: [[rc://en/ta/man/jit/figs-hyperbole]])
This statement implies that the apostles remained in Jerusalem even though they also experienced this great persecution. (See: [[rc://en/ta/man/jit/figs-explicit]])