This can be understood a couple of ways. That each player can only vote once, and then can't vote for any more proposals for the rest of the game. Each player may only vote once per proposal. All rule-changes proposed in the proper way shall be voted on. They will be adopted if and only if they receive the required number of votes.
Every player is an eligible voter.
Every eligible voter must participate in every vote on rule-changes. Now, rule changes were made the proper way, so they need to be voted on. And, every player MUST participate on every vote for rule changes. The only way that this can occur is if players have one vote per proposal. For even more clarification, I look at game custom.