Here in verse 27, the 1840 edition replaced the relative pronoun that with who. The reading of the 1837 edition, the copytext for the 1840 edition, shows that the 1840 change from that to who made the entire passage read with only who as the relative pronoun (the original that is marked below with an arrow):
The 1840 change may, in fact, have been unintended. In any event, the 1908 RLDS edition restored the original that to the RLDS text, most probably by reference to 𝓟. The critical text will, of course, maintain the original that here in Alma 19:27; the original use of which will also be restored for the four cases in this passage that were changed to who in the editing for the 1837 edition (only the first instance of who, in verse 25, was original to the text). For further discussion, see under which in volume 3.
Summary: Follow all the original forms of the relative pronoun in Alma 19:25–27 (four cases of which and one of that); the original text showed considerable variation in the selection of the relative pronoun, with instances of which, who(m), and that.