In 1 Nephi chapter 2, Lehi wished that Lemuel would be steadfast and immovable in keeping the commandments of God, and that Laman would be continually running to the fountain of all righteousness. This infers, to me, that they did keep the commandments at times, they were just inconsistent and wavering. This is emphasized by the fact that right after they saw the angel who told them the Lord would deliver Laban into their hands, they began to doubt and fear, and thought their task was impossible.
Lehi didn't ask them to start keeping the commandments or to begin running to the fountain of all righteousness, but to be steadfast and to continue.
Nephi, on the other hand, knew that if the Lord gave a commandment, then it wasn’t an impossible task. The Lord would be there to help you accomplish it, if you had faith. (1 Ne. 3:7)
I try really hard to remember that, and to keep faith in the Lord when He commands. But I could certainly do better, especially when things get hard, at remembering this, and that the “tender mercies of the Lord are over all those whom he hath chosen, because of their faith, to make them mighty even unto the power of deliverance.” (1 Ne. 1:20) He delivered the sons of Lehi from Laban, and delivered Laban into their hands so they might fulfill His (the Lord's) commandments. He will do the same for us, if we have faith. All my life I have seen, again and again, examples of this-- the Lord will help you keep the commandments He gives you.