Both of them are the main players in their clubs, while both Juventus and Napoli have a lack number of center-backs. I am not sure Chelsea can sign both De Light and Koulibaly. I think Juventus and Napoli don't want to risk their defense strength by selling their main center-back. Moreover, I never heard that De Light and Koulibaly are unhappy in their current clubs. So, Chelsea seems to have a small chance to sign those center-backs. If there is another option, I think Chelsea needs to consider other center-backs.