Hi Michelle, and welcome to planDisney!
Congratulations on snagging a reservation to assemble a Custom Astromech Unit at the
Droid Depot at
Disney’s Hollywood Studios for your daughter! That whole experience is one that no one in my family will forget because it was so much fun!
You are correct; your daughter will be able to bring her brother in with her, and he will be able to assist her, but ultimately, your daughter will make all of the decisions as to the look she desires for her droid. When my two children were able to build their Droids, my husband and I were able to assist with no problems. Besides, how much fun is it really to just watch, right?
Do not forget that after you assemble your droid, additional accessories for more customization options are available for purchase. I recommend browsing that section as you will be surprised at what cool items you find.
Please return should you have additional questions prior to your arrival.
Have a magical experience!
Raquel