i do sympathize with your struggles, but i think some idea of what you would live to convey with these designs could be helpful ^^' apart from how these characters relate back to you, could we please have a general idea of what these characters are like in your story?
i'm not entirely sure how to help you on this, but i will say since king lucifer has a lot of black in his design, putting a light grey outline for his hands and legs could help? i see this a lot but with characters that are very dark-colored, it's important to give some clarity to the design and make sure people can see parts of their body.
i like gabriel though, the soft purple pairs well with the gold in his design! best of luck in your comic!