multiple accounts attached to 1 email

My team is trying to send out retention based messaging to our customers, reminding them to pay their bill, submit necessary documentation etc. In the event that a user signed up for 2+ plans but used the same email address, is there a way to distinguish these in the email? 

For example, say individual A bought 2 plans, 1 for themselves and 1 for their child, using the same email. When the plan for their child is about to expire, but not thier own, how can we send a reminder to renew that specific plan?