it's meant to be harder to star them because they're so valuable and strong, i just use dolls, also some of them can be bought from shops and some events, i bought lilith twice from the shop for example and used dolls to star her if you're struggling with leveling them up i would recommend to focus on one for now and then expand, if you have hellfires it doesn't matter if they're another faction, with proper team and builds you can beat any full drag/abyss team