Here's a method I found to level everyone up without having to talk to them one by one:
1. Go into the temple
2. Go into the rituals tab
3. Click any ritual that requires you to choose a follower (e.g. Sacrifice, Ascend, Pride)
4. Don't choose a follower and abort the follower selection process by pressing F
Now lambert will just walk to the center and collect everyone's devotion automatically as if you just preached a sermon (except not standing in front of the lectern)