Hoping someone can help with a couple of questions.

Our dates are September 24th (late flight, no park day)-October 1 with 4 people in our room. DH & I will be in the parks for all 7 days, the other 2 persons in our room have other plans 2 days out of the 7 days so will only be in the parks 5 of the 7 days. Because we are all in the same room and our tickets all have to be the same, we only booked our trip with 5 days tickets and DH and I are going to upgrade our 2 tickets to 7 days once we get there. Since we only have 5 day tickets but our room is for 7 nights/8 days: [*]Can I only book FP+ for only 5 days or will I be able to book for all the days? [*]If I can only book for 5 of the 8 days, once I book 5 of the days, will the other days just be greyed out? Just trying to understand what to expect. Thank you in advance