There are 2 options to add family members who want to train with TheStack hardware.
Option 1: You can add a family member to train on their own iOS device, just as you are. To do that, simply have that family member download the App and activate the same serial number you did. This will in no way impact your training data, and we allow a serial number to be activated several times for this purpose.
https://www.thestacksystem.com/apps/help-center#hc-i-have-thestack-hardware-how-do-i-get-started-training
Option 2: You can add them as 'Local Golfers' - on your iOS device, under your Apple ID login. To do that, here are the steps:
1) Click Profile (top right)
2) Click on Stable of Golfers
3) Click 'Add Golfer' (top right)
4) Click 'Add a Local Profile'