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
We love hearing from you! Support can be reached at firstname.lastname@example.org or by phone at (872) 814-6308. Our office hours are 9am-5pm Monday - Friday and 9am-4pm EST on weekends.