This is really common! Separate parents usually want to split payments between them and not be responsible for the other parent.
Here's how we recommend you do it in Groundwork.
First, talk to the parents and agree how payments will be split. Do they each want to pay half of every payment? Or, do they want to alternate payments?
Second, add two versions of the player to the team. For example, "Johnny Jones - Mom" with mom's email and "Johnny Jones - Dad" with dad's email. Then customize each player's payments. You can delete payments or edit each payment amount.
Finally, send the invitations to each parent and let them know they each need to sign up and are responsible for their own payments.