Here scribe 2 of 𝓟 initially wrote “according to their own will and pleasure”, which is what we expect in modern English. However, somewhat later he inserted the plural s at the end of will. The word will is found here at the end of the line in 𝓟, with the inserted s somewhat above the line and written with a weaker ink flow. There is clearly no reason for scribe 2 to have corrected will to wills except that the original manuscript must have read in the plural. The 1830 compositor, however, set the fully singular “will and pleasure” for this passage.
We find further support for the plural usage later on in the book of Alma. Here the scribe in 𝓟 was the same scribe 2:
Once more scribe 2 initially wrote “will and pleasure”, what we expect in modern English. He soon corrected the text by inserting an s after will and one after pleasure. Not liking the result, he erased the s that he had just inserted after will, then decided that the s was indeed in the text and wrote a second time the s after will. Clearly, the original manuscript here read “wills and pleasures”. The fully plural reading in Alma 12:31 suggests that in Alma 4:8 the original text may have also read as “wills and pleasures”. Interestingly, the difficult reading in Alma 12:31 has never been edited to the singular “will and pleasure” in any of the printed editions.
When referring to one individual, the Book of Mormon text has only the singular “will and pleasure”:
There are only two instances where the text refers to the “will(s) and pleasure(s)” of more than one individual—namely, in Alma 4:8 and Alma 12:31. Thus the plural usage seems intentional when referring to more than one person.
Early Modern English provides quite a few examples of such plural usage. Literature Online gives the following examples of the plural usage when referring to the will and pleasure of more than one person. All of these examples date from the 1500s through the 1700s (spelling here regularized):
wills and pleasures
wills and pleasure
will and pleasures
Thus there is nothing inappropriate about the fully plural “their wills and pleasures” in Alma 12:31. Of course, the fairly frequent occurrence in Early Modern English of “their wills and pleasures” suggests that the singular pleasure in Alma 4:8 could be an error for pleasures. But the 1661 example from Percy Herbert provides evidence that even “their wills and pleasure” is possible. Note, by the way, that Herbert is also responsible for an example of the fully plural “their wills and pleasures”. Given these citations, the critical text will restore the original “their own wills and pleasure” in Alma 4:8 and maintain the even more difficult but intended “their wills and pleasures” in Alma 12:31.
It is worth noting here that the King James Bible never uses the phrase “will(s) and pleasure(s)”, in the singular or plural. There are, however, three instances involving both will and pleasure that are similar in meaning to “will(s) and pleasure(s)”:
The plural “wills and pleasure(s)” may represent one more example of Early Modern English in the Book of Mormon text, usage that had become archaic by the 1800s, as evidenced by the tendency of scribe 2 of 𝓟 and the 1830 compositor to replace the plural with the singular in this expression.
Summary: Restore in Alma 4:8 the corrected reading in 𝓟, “their own wills and pleasure”; also maintain the fully plural “their wills and pleasures” in Alma 12:31; such plural usage seems to have occurred fairly frequently in Early Modern English, providing it referred to the will and pleasure of more than one person.