When I layer two necklaces with the same chain, I hook both necklaces together to make one long necklace. I can then position whichever necklace I want on top and the other one on the bottom while I wrap the new “giant necklace” around my neck. They never tangle with me this way. I use this method for 2 DBTY and necklaces with a similar weight, chain style, and length.
Another method I use to layer is to wear a heavy pendant, like a VCA Vintage Alhambra, and layer it with a shorter pendant that is much lighter, like a DBTY. With the difference in length and weight, they shouldn’t tangle too much.
I hope this helps you guys!