Since the Premium service for Everlance would be considered an "in-app purchase", this feature cannot be shared across members of a family using Family Sharing. An Everlance Premium purchase is applied to one account only and cannot be shared with other accounts. Also, you can only change the payment information from the Family Sharing Manager's account.
More information on Family Sharing: https://support.apple.com/en-us/HT203046
If you need to contact support or have questions, please check out our help center at help.everlance.com or reach out at firstname.lastname@example.org or by phone at (872) 814-6308 (USA) or (877)704-2687 (CAN). Our office hours are 9am-5pm EST Monday - Friday and 9am-1pm EST on weekends.