𝓞 is extant here and has the preposition in at both the beginning and ending of the relative clause: namely, “in whatsoever land they may be in”. The 1840 edition removed the beginning in, perhaps accidentally. The 1908 RLDS edition restored the original beginning in, apparently by reference to 𝓟. On the other hand, the 1920 LDS edition removed that in, possibly by reference to the 1840 edition but also perhaps independently since the repeated in is ungrammatical in standard English. The 1920 removal of the in was intentional since its deletion was marked in the committee copy.
The critical text will restore the original beginning in, especially since elsewhere in the original text relative clauses of this form seem to have consistently had both the beginning and ending in. For discussion and examples, see under Alma 23:1; also see the discussion under 2 Nephi 2:22.
Summary: Restore in Alma 26:37 the preposition in at the beginning of the relative clause; the original text had in at both the beginning and ending of this relative clause (“in whatsoever land they may be in”).