If a player has two parents, the second parent will have to make a separate account, register with the team, and then be added (by a site admin) to the proper groups for that team.
It would be nice if users that have been authorized for the team (say coaches and team managers) could send people a link that would cover all three steps.
Clearly it would need to be a one-time key - associated with the recipient's email address - so that it could not be shared, etc.
|Frequency||Several times a year|
Any communication that is sent to a rostered player will also be sent to any linked account so you don't need to manually add them to the team or to the group. Additionally, if the team page is private, linked will also have access once the player is rostered. Here are a couple of help articles that talk about linking accounts