Hi Mike,
Thanks for submitting this idea!
Here are a couple of thoughts for you.
Have you ever used text message invites? You may have more success with those, especially if emails to the family are ending up in their spam folder.
It is possible to add a link or button to your website that would direct the family to the planning center login.
This is the link you would use: https://plan.passare.com/planner
Let us know if you'd like for us to help with any of this.
Passare Product Team