Cannot comment to those resources have not used them.
Can share this~
Our trainer came out with the team for a couple of weeks to help us learn to use stretching partners for certain stretches.
Better stretch angles, resistance, applied pressure.
Of which, for me, did not feel comfortable doing because uncertainty of what the partner might do, it can take a player Beyond healthy perimeter and never felt right putting pressure on another person's body that might also injure them.
Others liked it tho.
Will add that stretching before workouts, practice, game days is necessary, it is also important to stretch a little afterwards to.
Perhaps some others have examples to add about healthy stretching..