How to handle a fight situation?

Ok I am 16 years old (male). I am not really big, but I work out alot and stay in shape. I am pretty ripped up, and I am very strong for my size. I am in the 11th grade. Anyway, some older guys got in trouble last weekend about fighting. 2 guys who graduated and a senior was meeting some other guy at a gas station and was going to fight him, but a cop showed up in the guys truck instead and caught them. The driver of the three guys had a gun and other weapons in his car. So anyway, the guys 15 year old brother sent me a message on facebook and was like what you been saying about my brother and I was like nothing. He was like I heard you have been telling people about him getting in trouble and I was like no but everyone already knows. So he was like well I heard you dont like him and I was like I havent talked to him in like a year so how can i not like him, is your bro pissed at me? And he was like well if i keep hearing crap im gonna be pissed. I was just like maybe the person your hearing it from is starting stuff. then he got offline. I know i could take this guy pretty easily, but if I have to fight him, he will probably get his bro and all his bros friends to try to fight me. Im not sure if this will turn into a fight or not, or if it was just an exchange of words or what it was. But I dont care to fight the 15 year old but his brother is like 19 or 20 and his bros friends will probably jump in. I cant run away and I cant tell on them because I will not get a rep like that. Im thinking Im about to get to the point in life where Im just going to man up and fight anybody that wants some no matter how old or big. And by the way, the 15 year olds brother is not big at all. Im bigger than him and I think I might could take him, but I dont think he fights fair. I have only been in one real fight, never took lessons or anything, but the one fight I won. I grappled my 18 year old cousin and won by choke and my friend that is like 6 foot 5 and won by arm bar. Thats about all I know about my fighting skills, so idk how good I am. The guy I fought wasnt a big deal, he just slapped my out of no where so we fought. What should i do guys?