i think fooling around in incest is always pretty hot, though with brothers you're almost as equal as can be without the constraints of labels like father or son put on you
there'll always be sibling squabbles as brothers, though it's usually resolved amongst yourselves and i think that chemistry born from having to communicate and understand one another adds that interesting layer of intrigue, not solely because you're just related, but because you also know the worst parts of each other and still maintain a precedent that you can experiment if no one else is available because you'll be there for one another
it's kind of similar to using a family member's used fleshlight, or helping out your brother or dad with a load if he's divorced or has been broken up. you do it as a gesture of comfort because they know you, almost to an intimate degree, and small things like this allow you to fool around without the idea having to be made from a direct spoken gesture of, "hey, do you want to fool around?"
having a motive that allows you to act without feeling as though you're confessing is safer in that kind of situation because there's a mutual idea, a thing you both want that can be put in the way of reason which allows you to ignore the severity of the incest, and that what you're doing isn't normal.
Obviously it isn't, but you settle. You see the situation as just a one time thing, or a rarity at most, and because of it not being normal, it's enjoyed all the more between you the wronger it is and the more you love each other.
though if you were to act from feelings without a reason in the way, perhaps someone just has a huge overwhelming crush on their brother and they want to fool around sexually oh so bad, then the sensitivity of the question is subject to your own relationship. Do you usually have deep talks with him? Do you understand each other well, or are you more distant? Is he even gay?
That distance can be used as a landmine, and by distance, I mean how close you are to each other perhaps emotionally, physically, or even sexually.
to either be weary of it's existence and not wanting to cause a conflict between you but still wanting that connection is longing. You know you want it, perhaps his own feelings are unclear, or there's something preventing you from being with one another.
or perhaps you've already stepped on the landmine, and now that you're caught in the midst of it, you can't say what you truly want to or you'll be the one to cause that boom. You're already fooling around, but some kind of slip up- perhaps revealing that hooking up like this is more emotionally impactful for you might just ruin things between you, or cause an upset in your relationship that would change things forever.
There are so many factors to consider when making these situations that i think bring the over all appeal to incest in general. There're a lot of modifiers that set different tones very easily, and from them you can make a variety of stories and scenes.
By 'fooling around' at least, that makes me think of a noncommittal fling between two brothers that, because of a lack of communicated serious intent, leaves both parties leeway into the excuse of it just being convenient. It's available, and if there was more to it, well, they couldn't say for sure because it would mean acknowledging there's more between them than it just being a tryst between men who live under the same roof.
