Why does my brothers steal girl clothes?

The first brother I will start with is David (just a cover name) when he was around 13 to about 14 years old he would steal my sisters clothes and hide them under his dresses. When we found them they would be wet as if he put them in the shower, they didn’t smell or anything just wet. But he did stop after a while. My other brother on the other hand Charlie (also a cover name) he also did the same thing age around 6 or 7 but with my step mom’s clothes. Now he’s about 13 and steals my mom’s thongs and wears them in secret.