The 1841 British edition accidentally replaced the existential there with the subject pronoun they, probably under the influence of the preceding and following instances of they: “and they had all things common among them ... but they were all made free and partakers of the heavenly gift”. The 1920 LDS edition restored the correct there. Interestingly, the 1953 RLDS edition made the same change from there to they, probably independently. For other cases where there has been replaced by they, see under 3 Nephi 7:2–3.
It is possible that the there of the earliest textual sources (the 1830 edition and the printer’s manuscript) is a mistake for they (although the original manuscript itself very probably read there). During the dictation of the text, the existential there could have entered the text under the influence of the immediately preceding therefore. But in support of there, there are other examples in the text of the negative existential there were not:
The second example is particularly relevant since the following yea-clause has the pronoun they (“yea they were not half so numerous”), thus giving an example like 4 Nephi 1:3 where the passage switches from the existential there to the pronoun they. There is consequently no strong reason to emend the there in 4 Nephi 1:3 to they.
Summary: Maintain the earliest reading in 4 Nephi 1:3 with its original existential there: “therefore there were not rich and poor / bond and free”.