Is it permissible to change one's place during the Friday sermon if the Imam's voice is unclear, given the possibility of stepping over people's necks, and would that or speaking be considered idle talk (laghw)?

Moving within the mosque to listen to the sermon is not problematic, as long as it does not harm Muslims by stepping over necks. Stepping over necks is prohibited, except to fill a gap in the row, which some scholars have permitted. As for forbidding speech during the sermon, there are two opinions: The first: forbidding speech absolutely, whether one hears the sermon or not. The second: if one does not hear the sermon, speaking is permissible. The more cautious approach is to refrain from speaking absolutely.