I am writing a series of five novels, and they centre around four couples. Emily and Daniel, Jake and Yvonne, Cara and Andrew, and Sasha and Marvin. I am so totally in love with the first three couples, and I feel like I really understand them as characters, but I feel like Sasha and Marvin are lacking character development. I don't know if I should just get rid of them or not. I mean, I love Sasha, but I'm not sure if she has a purpose. And I can't really get rid of Marvin, he plays quite an important part, but I don't really like him that much. I'm really struggling with this, I have been working on this project for a long time now, and it is really upsetting me. Killing off a character is one thing, but getting rid of one altogether is quite devastating. These characters have become very close to my heart, so what I'm basically saying is, how do you develop a character well? What should I do in order to understand Sasha and Marvin? I had no trouble with the others.
Hard to say, since I don't know the overall plot line, but it might be useful to have a character or two even you as the author find unlikeable, just to keep the pot boiling. We need some conflict, right, or we have no story. Or by "don't like" do you mean you don't like the way he's not shaping up, as in he refuses to be more than an inchoate blob? If he plays an important part, I doubt that. Think about how and why his role is important and get to know him beginning with that. As for Sasha, keep an eye out for something for her to do. Over five novels, there has to be something.
If you dislike him, he could become a villain? If you don't know your character, you may want to modify the person he is, and make him more interesting?
I'm crossing threads here, but I think the thing to do is go to a hotel and pretend you are Marvin for a weekend. Let us know how that goes.
