Can I hold one point for 7 points then gank the other to win the game or do I need to occupy both to win?

Yes, you can win the game by holding one battlefield to reach 7 points and then ganking to conquer the second battlefield in the same turn. You do not need to occupy both battlefields simultaneously to win.

According to Rule 448.1.b.2, when you are at 7 points, you can score the final point through a "Conquer" action if you have scored every battlefield through either method (Hold or Conquer) during that turn.

As confirmed by RiftJudge FAQ #6708:

• Sequence:
  1. You score your 7th point during your beginning phase by holding the first battlefield.
  2. You move a unit with the Ganking ability to the empty second battlefield, conquering it.
  3. Because you have now scored every battlefield this turn (one through Hold, one through Conquer), you score the final point and win immediately.

The requirement to "score every battlefield" applies to the turn in which you are attempting to win, not to the requirement of holding them simultaneously.