Welcome to planDisney, Sarah! It's so nice that you found us here on our little corner of the internet.
As long as you are connected to this Guest through the 
My Family & Friends list, you should be able to purchase and reserve Lightning Lanes for them through 
Lightning Lane Multi Pass and/or Lightning Lane Single Pass. However, there is no guarantee that you'll be able to book the same reservations as availability will likely have changed. If you want all the members of your travel party to have the same reservation times, you may want to wait to make your reservations until 3 days out. Or, make your initial reservations 7 days ahead, and then try to modify them all to match 3 days ahead.
There are a few experiences that I would place at the top of my priority list when it comes to making 
Lighting Lane Multi Pass reservations. In 
Magic Kingdom Park, I would either make 
Tiana's Bayou Adventure or 
Peter Pan's Flight my pick from Group 1. For 
Disney's Animal Kingdom Theme Park, it's 
Na'vi River Journey all the way! When it comes to 
Disney's Hollywood Studios, it's hands down 
Slinky Dog Dash. And with 
EPCOT, it's 
Remy's Ratatouille Adventure. But all that being said, it's all about what speaks to your group. For example, while both Frozen Ever After and Remy's Ratatouille Adventure in EPCOT are amazing rides and can rack up long waits, Remy's Ratatouille Adventure often has a longer wait...but I still usually choose 
Frozen Ever After because it makes my heart happy and it's a must-do for every visit. Some things are worth melting for!
Sarah, best wishes with your Lightning Lane reservations. Have an amazing trip and be sure to 
reach out with any other questions that you may have!
Love's a force that's powerful and strange,
Matt