Here in his editing of the text for the 1837 edition, Joseph Smith decided that the second which refers to the people of liberty (and also perhaps the brethren of Parhoron); Joseph therefore grammatically emended the which to who. But in actuality, it was the results of the election itself that put the kingmen to silence (at least for the time being). Here the entire initial statement “and Parhoron retained the judgment seat” is modified by two sentential relative clauses (listed above as 1 and 2). The first one refers to the rejoicing of the winners, the second to putting the kingmen to silence. The text is not claiming that the people of liberty had to do anything more (at least at that time) to silence the kingmen. The critical text will therefore restore the original which here in Alma 51:7. Of course, any original which would be restored in the critical text anyway, even when it corresponds to who or whom in modern English. For further discussion of the editing of which to who(m), see under which in volume 3.
Summary: Restore the original which in Alma 51:7; in this case, the which does not refer to people but instead heads a sentential relative clause.