If you want to sign up two people, then include "1" in the guest field. For three people total, include "2" in the guest field. And so on...
This is true regardless of whether someone is a member or guest of that member.
The event flyer states that you can sign up members and up to two guests through July 23. This means that someone with an individual membership can sign up themselves and two guests for a total of three people through that date. A dual membership can sign up the two dual members and two guests for a total of four people.
