The way SE is set up is the Guardian (G1) should have the USAV Membership of the athlete on their account. In order for another parent/guardian(G2) to be able to participate in the app, they must be invited by G1 to be a guardian. Please see the instruction through the link below on how to add a guardian. Once G2 accepts the invitation they will also be able to participate on the app.
For athletes who have their own SE account:
For an athlete to participate on their own account in the SE app, she too will need to be added as a guardian to themselves. Please use the guardian instructions below to invite them.
If the athlete holds the membership under her account she will need to log in and invite guardians for her profile in order for you to be able to participate on the app.
I have had several conversations with SE regarding how they have Households set up in and what that looks like for athletes to have memberships and they are working on improving this. It is a major change for them and will take some time to develop and test before they release it. I will say they have done a lot since last year to fix issues and are working on them.
To invite a guardian to your account so they can participate on the SE app for your team please use the following link.