Erik's feelings toward Adin appear to be fairly mild. He ranges from being mildly amused and affectionate to being mildly annoyed and threatened. (Adin just purely adores Erik, no matter what.) Now that Adin is more mobile, he crawls toward Erik and whatever Erik is doing. Erik instantly responds with outraged, "no, he'll ruin it" or "I'm using this" or "no no no no no". I can pretty much persuade him that Adin doesn't mean him any harm, that he can offer Adin another toy, that they can take turns, etc. Also, if Adin makes it close enough he will touch Erik which Erik also protests.
Today at naptime, Erik was laying in his little toddler bed and Adin crawled over, pulled himself up and stood there reaching for Erik. Erik must have been overcome with affection because he reached over and gave Adin a one armed bear hug that lasted so long I had to separate them. I couldn't have been more delighted.