I never could understand why it's such a big deal

I'm not from the US but from Central America. I haven't been in a sexual relationship with any of my siblings but I have pleasured myself in front of them. I have a brother who's like 9 years younger than me and ever since he saw me pleasuring myself he started doing it in front of me or also watching me while I do it. I also have 4 sisters and 2 of them have asked me to pleasure myself in front of them before, they wanted me to get erect so they could see my penis. I have another sister who's older than me and we have kissed like 3 times before in a sexual way but never had sex, now she's married so I would never do that again. I'm also in a relationship and I have a son but I'm kind of scared that my son might start doing something like that when he gets older, I don't know what to think of it, what do you guys think?