(19m) Grew up in a nudist household - but lately things have gotten weird

My mom (45f) my twin sister (19f) and I have always been nudists. My mom raised us this way in the household. It was very common for me and my mom to hang out naked; same with me and my sister. Whether swimming, hot tubbing, getting ready…it was just…normal.

There was never anything sexual about it….until recently. Or so it feels.

First of all, over the past year, my sister had grown some absurdly big boobs and wide hips. She used to be super skinny but she had really filled out.

Because of this, for the first time in my life, I got a huge boner in front of my sister and mom when we were in the hot tub. I tried to hide it but I couldn’t, and when I stood up they saw it.

My mom said it was totally normal….but it now happens pretty much everytime I see my sister naked.

I also feel kinda weird about how they looked at my dick. It felt….a little too …idk….lustful.