Membership credits cannot be shared automatically between clients, but shared credits can be easily accounted for within the account.
To account for a shared credit, the credit will first need to be removed from the member's client record by editing the available credit down by 1 through these steps:
Editing a Client's Membership Credit Balance
Then store credit will need to be added to the other client's record in the amount that will cover the cost of the service they are receiving. Store credit can be added through these steps:
Store credit can be applied during check out through these steps:
Applying Store Credit During Checkout
Store credits is not viewed as income. So these steps should be followed rather than choosing any other payment method at check out so you do not duplicate any income generated.