If you need to make adjustments to the family while the account is still in pending, you have the ability to remove the student before completing the account's enrollment. This way the student will not show up in the account once the account is made active. 

In the Pending Families view: 
1. Click the family name
2. Click Student Information 
3. Click the orange "Remove" button next to the student who you would like to remove
4. Click Save. 
From there you can complete enrollment for the student(s) that remain on the account. Please refer to the Knowledgebase article How Can I Complete Enrollment From Pending Families?