Hi
The stickys at the top of this page help in knowing what to do on this Forum.
Basically you decide what type of design you are looking for and you then post on someone's thread requesting they make the design (and add personalization).
Each designer has different rules so please read the first post of their thread.
Many do not post "blank designs" due to theft.
With 14 people going I would stick to buying a different group color for each theme park.
Example:
Red or White for Magic Kingdom
Blue for Disney Hollywood studios
Green for Animal kingdom
White for Epcot.
So then you have to decide are you going with a "Family name" ,,like
"Jones Family Trip or ,Vacation"
Walt Disney World
2016
OR
First names(Jon,Patty,Mike,Patty,Allison) etc
Do you go with individual characters or a group of characters.
If you have never made t-shirt iron on transfers I would suggest a group design with a family name and the year.
Hope this helps
feel free to ask more questions
Hugs Mel