Hiya, Melina! I'm glad to meet you at planDisney, but your question has Alice in Wonderland echoing in my head:
'Curiouser and curiouser.' Let's hop through the Looking Glass and see what we can discover.
Since you are booking your
Lightning Lane passes three days ahead of your
Walt Disney World Resort visit, I assume you are not staying within the
Disney Resorts Collection. If this is the case, you should be able to book Lightning Lane passes for the 3-day tickets three days before the first date on that ticket for any day within the ticket's eligibility window. For your day in the shadow of the majestic Cinderella Castle, you can book your
Magic Kingdom Park passes three days ahead of that day. With two separate tickets, you will have two different eligibility dates to purchase passes.
I have no idea why one person would be able to book all four days unless they are staying at a Disney resort, as one of the many benefits of being a resort Guest is the ability to book Lightning Lane passes seven days ahead for the duration of your stay (up to 14 days).
If you want your passes coordinated with the same Lightning Lane entry times, you may want to wait until three days before heading to the Magic Kingdom, when you are all eligible to buy them.
I hope this information on the two dates helps uncover why you can only book three days now. I wish I had more than a guess on the fourth Guest being able to access all four days. If you have any challenges when you go to buy passes for the Magic Kingdom once you are eligible, you can call
My Disney Experience, MagicBand and MagicBand+ for assistance. Cast Members at this line can check your account to see if any curious things are happening.
If you have any other questions, we're always happy to help at
planDisney!
Wishing You a Magical Adventure!
Jana