That seems like a rather myopic way to view the conversation. The final few statements are broken into three distinct thoughts:

“When gone am I, the last of the Jedi will you be.”

“The Force runs strong in your family…pass on what you have learned.”

“Luke, there is another Skywalker.”

Each thought builds on the one before it, but it’s important to preserve the order of lines. Luke is being commanded to pass on what he has learned without first knowing that he has another living relative. It could be implied that Luke would pass on his knowledge to his children, or that his knowledge would lead to a ‘return of the Jedi’ in the galaxy like the title implies. Only after this order does Yoda drop the ‘other Skywalker’ bomb on him, so it stands to reason that this other would be among those Luke teaches but almost certainly not the extent of his obligation. I know I’d be pissed as a Force Ghost if my student just trained the secret twin and nobody else because of the letter of the order and not its spirit.