As explained under Alma 17:6, the plural minds is possible in the Book of Mormon text, although modern English speakers expect references to “the mind of the people” rather than to “the minds of the people”. Here in 3 Nephi 7:14, the 1874 RLDS edition made the change to the singular mind, but the 1908 RLDS edition restored the plural minds (most probably by reference to 𝓟). For each case of mind(s), the critical text will follow the earliest reading.
Summary: Maintain the plural minds in 3 Nephi 7:14, the reading of both 𝓟 and the 1830 reading (and the probable reading of 𝓞).