The 1830 typesetter changed the singular kindred of the printer’s manuscript to the plural kindreds. In current English, kindred is singular in form but takes plural verbs (such as “my kindred are …”), although in actual speech kindred would be considered archaic or dialectal. The preferred term today is the regular count noun relative (as in “I have many relatives and friends”).
Elsewhere in the Book of Mormon text, we have instances of the form kindred with either the singular meaning ‘relative’ or the plural meaning ‘relatives’:
singular kindred ‘relative’
singular kindred ‘relatives’
There are also instances of the plural kindreds with the meaning ‘relatives’:
plural kindreds ‘relatives’
Finally, there are two cases in 3 Nephi where the scribe in 𝓟, Oliver Cowdery, wrote the plural kindreds, but the 1830 edition has the singular kindred:
For both of these cases, 𝓟 and the 1830 edition are firsthand copies of 𝓞. See under each of these passages for discussion of which reading, the singular kindred or the plural kindreds, represents the original text.
The 1830 change from many kindred to many kindreds in Alma 10:4 is probably the result of the preceding plural many; otherwise, the text has the plural kindreds when preceded by many (in 3 Nephi 6:27 and 3 Nephi 7:4, listed above). Even so, there are eight occurrences of the singular kindred with the plural meaning ‘relatives’ that have never been changed to kindreds. These examples show that the singular kindred in 𝓟 for Alma 10:4 is perfectly acceptable. The critical text will therefore restore the singular kindred, as did the 1908 RLDS edition (based on the reading in 𝓟).
Historically and dialectally in English, the singular kindred has been used as a plural count noun, much like the word people (as in “many people are coming”). Here is an example of many kindred (the original language in Alma 10:4) listed in the Oxford English Dictionary under flowerist:
In this case, kindred refers to related plants rather than related people.
Summary: Since either many kindred or many kindreds will work in Alma 10:4, the critical text will restore the earliest reading, many kindred (the reading in 𝓟).