Here the 1953 RLDS edition added the infinite verb form be, replacing “there should a band of Christians remain” with “there should be a band of Christians remain”. This secondary reading appears to be grammatically wrong. There is a similar example of such an intrusive be in the LDS text, beginning with the 1905 LDS missionary edition:
The construction “there should NP ” (where NP stands for a noun phrase) is a fairly common construction in the Book of Mormon text. Dispersed throughout the rest of the original text are seven more examples of this construction (of which five involve negation):
Thus there is no need to insert a be verb in either Alma 46:13 or Ether 6:5. In fact, it is wrong because the following verb takes the infinitive form. There are cases of this construction where be does occur as an auxiliary verb, but in all instances that verb is followed by a past-participial verb form (so that we end up with a passive construction):
The last example has a long relative clause after armies and in the original text ends up repeating the verb phrase should be; see the discussion under 3 Nephi 3:14.
The intrusive be here in Alma 46:13 and in Ether 6:5 may be due to the influence of the construction “there shall be NP ”, which is found in the original text. For discussion of that construction, see under 2 Nephi 1:6 and Helaman 14:5.
Summary: The critical text will follow the original expression “there should NP ” in Alma 46:13, Ether 6:5, and wherever else the earliest text supports it; there is no need for a be after should in any of these cases.