Hi Emily!
Thank you for bringing your question to the Disney Parks Moms Panel!
The 2013 Walt Disney World Marathon was my first ever marathon, so I think you've made the perfect choice for your first 26.2! My friends and I have also been making our own
2019 Walt Disney World Marathon plans this week. I'm already getting excited!
As
Walt Disney World Annual Passholders, you and your husband can register during early registration, but it's technically for passholders only. While it may be possible to register others once you open the link, runDisney only allots a certain number of spots for passholder registration, so registering someone without an annual pass would be taking spots away from those that have them.
I don't think your sister and brother-in-law should have any trouble getting in once it opens to the public. Right now, it's scheduled to open on April 17, 2018, at noon ET. Here is a link to a
blog post with tips for registering for runDisney events.
I hope this helps. Please let me know if you have any other questions and good luck at your first marathon!
~Lori