The 1858 Wright edition replaced “these people” with “this people” here in Mormon 5:9. This change could have been influenced by the later occurrence of “this people” three more times in this verse:
Normally, the Book of Mormon text has the more expected “this people” (221 times in the original text), but there is nonetheless one other occurrence of “these people”:
Moreover, there are 11 instances in the original text of the parallel demonstrative plural “those people”. So “these people” is definitely possible in Mormon 5:9 and will be continued in the critical text since the earliest textual sources have the plural these.
Summary: Maintain in Mormon 5:9 the infrequent “these people”, the reading of the earliest textual sources.