Ram isn't with anyone, she cares for her sister and sees Sin as a friend and family. I have yet to see anything that would hint they are romantically involved. It isn't the same as with El and Sol where there are blatant hints. Caring about your friends doesn't mean you love them romantically. You gotta also remember Ramlethal is new to the whole caring about others thing, so it would be easy to get the wrong idea as to her feelings for both her sister and Sin. If anything, Sin is more of a big brother to her, with Sin acting that way and not showing any hint of romantically liking Ramlethal as well.
Ram isn't with anyone, she cares for her sister and sees Sin as a friend and family. I have yet to see anything that would hint they are romantically involved. It isn't the same as with El and Sol where there are blatant hints.
The only reason that Sol even cares is that Elp reminds him of Aria, somewhat. Once Jack-O enters the picture and completes her merge with Justice, Elp is just someone to be saved at that point. There is no real romantic tension between them aside of bring up the memories of Aria, a space that Jack-O fill almost completely.
Sin acting that way and not showing any hint of romantically liking Ramlethal as well.
Sin, if anything, is really, really... dumb. Sol calls him "The Dumbass" for a reason. I honestly don't think that he would have much of a clue if Ram's emotions for him go beyond a friendship and I don't think that he would even understand his own (assuming that something IS there) for her. Even if she was being opaque about it which would be WAY out of character for her. (Love is an emotion that is complex... with her just beginning to explore her humanity through hers, I don't think she would have a grasp of the concept "love" and Elp would be a horrible teacher for that subject).