This is the one, correct? 8.7 Equip 4 Champions with three 4* or higher Artifact Sets 

Going to be three different 2 piece sets, each 4* or higher. Can you post a screenshot of the gearing you're using?

4x champions need to wear 3 sets of artifacts, meaning 6 pieces of the same set, all of which are 4* or higher and lvld up to 12.

 https://vlc.onl/  

You cannot have someone in 2 life pieces and 4 def pieces. You cannot have someone in 4 lifesteal pieces and 2 life pieces. You cannot have someone in 6 lifesteal pieces.