The footnotes to the LDS edition of the scriptures provide the following verses as an indication of the commandments to Lehi which had been fulfilled:
"1 Nephi 3:18 For behold, they have rejected the words of the prophets. Wherefore, if my father should dwell in the land after he hath been commanded to flee out of the land, behold, he would also perish. Wherefore, it must needs be that he flee out of the land."
"1 Nephi 5:21 And we had obtained the records which the Lord had commanded us, and searched them and found that they were desirable; yea, even of great worth unto us, insomuch that we could preserve the commandments of the Lord unto our children."
"1 Nephi 7:2 And it came to pass that the Lord commanded him that I, Nephi, and my brethren, should again return unto the land of Jerusalem, and bring down Ishmael and his family into the wilderness."
While all three verses are clearly commandments which are fulfilled, verse 8 appears to have relevance specifically to the command in 1 Nephi 7:2 to return for Ishmael. Following on the heels of the marriages in verse 7, verse 8 begins with "and thus." The marriages are therefore seen as a direct example of the fulfilment of a commandment. While the recorded commandment in 1 Nephi 7:2 does not specifically mention that they should bring Ismael's family and marry the daughters, there must of been that clear implication.