You have to get game and get naked in front of them. Most teenage boys under 16y/o are very sexually curious and like to get naked with their friends and do things like compare stiff penises. They generally are as curious as you are sexually about the other boys but are not game to be the first one to get naked. They are all scared if they go first the others will think they are weird but in most cases the other boys like the boy who will strip first and show themselves off. If another boy goes first most will get gamer and more trusting and strip off themselves.
I used to show my friends porn and talk about sex and they would get horny. When I felt sure they would be horny and had a stiff c0ck I would say "gee I am horny and I have a huge hard on". Then it is time to just strip naked and tell your friend that you love being naked and are always naked when home alone. Likely your friend will not be sure of what is going on but will likely be even more sexually excited seeing you naked with a stiff c0ck. Tell him to get naked as well. If he is nervous tell them not to be such a girl and get his off as well as it feels so relaxing, and all normal guys have c0cks and nuts and you aren't embarrassed letting him see yours. Hopefully he will be as horny as you are and will not take any convincing to get naked. I found many of my young teenage friends once they realized I was serious about relaxing naked with a hard c0ck in front of them were eager to get naked with me and generally from there we would do things like compare c0cks, have c0ck sword fights and masturbate together and even a few wanted to try some c0ck sucking. Even if they won't do it at first, stay naked as many will start to relax after a while and may change their mind and decide to join you being naked. I used to go skinny dipping with other boys in well hidden creek pools. Generally one would strip off their underwear while swimming and throw it up on the bank and relax naked. Generally another person would strip off their underwear as well, and then the others would do the same. In most cases the last couple boys would feel embarrassed that they would be seen as wimps for not stripping off and would finally do it.
Normal young horny teenage boys tend to be eager to get naked with their friends so the chances are very good that you can convince your friends to get naked with you and try some of the sexy things you want to try. But you have to relax and be willing to go first so they lose their nervousness and their horniness drives them to get their clothes off as well. If they see you horny and not embarrassed showing of your man bits generally they will relax and join you, Believe me most young teenage boys will join you naked if they feel sure no one else will find out they did it, so it may pay to assure them you are not going to tell anyone that they got naked with you. Good luck