Welcome, Maria
While non-Disney people may not understand, I can think of no better way to both remember and honor your husband and your boy's father than by visiting your family's happy place.
Guests visit
Walt Disney World Resort for all kinds of reasons, both joyous and sad. So you won't be caught off guard, you most likely will be asked if you're celebrating anything when both making and checking-in for resort hotel and dining reservations. If you're comfortable enough, you're absolutely more than welcome to say that you're celebrating your late husband's life, that you and your boys are on a healing trip, etc.
While there are currently no active opportunities to leave a permanent dedication at Walt Disney World Resort, there's a wonderful local organization called Give Kids The World Village. This whimsical resort provides cost-free, week-long vacations to families with children who have a life threatening illness. They have a commemorative paving stone program that comes with a certificate for you to keep, and your donation will help fund the Disney vacation of a lifetime for another family. (In their 'Give' section, look for 'Paving a Legacy'.)
Other ideas for just you and your boys: definitely enjoy his favorite Disney meals and attractions. Write his name on the the front of the complimentary 'I'm Celebrating' buttons, and each of you write a special message to him on the back that you don't share with each other. In lieu of a balloon release, purchase a classic Mickey balloon and pass it on to another family at the end of your vacation. (Write your husband's name on it as a special touch.) You could even have his name put on a special Christmas ornament that you pick out in his honor at one of Disney's Christmas shops.
I am so deeply sorry for your loss, Maria. I hope that this upcoming trip is filled with many happy memories for you and your boys.
~Kristen