For both these names, the RLDS text accidentally dropped an h. In the first instance, the final h was lost in the 1892 RLDS edition; this error has continued in the RLDS text. In the second example, the h after the m in Limhah was accidentally dropped in the 1874 RLDS edition (the resulting Limah is thus quite similar to the preceding Lamah). The 1908 RLDS edition restored the correct Limhah to the RLDS text.
The occurrence of final h’s in Book of Mormon names is very common (as it is in Hebrew names). And the h after the m in Limhah is found in other Book of Mormon names as well (namely, Limhi and Limher). So there is no reason to alter the spelling of these two names. For further discussion of h-final names in the Book of Mormon, see under Mormon 2:4 for discussion of the name Angolah.
Summary: Retain in Mormon 6:14 all the h’s in the names Lamah and Limhah, the earliest spellings for these two names.