Teach him there is a right and a wrong place to do it.
That's it.
No, is no.
And tell him, when he does it to you/your Husband, that is No.
AND to his sister.
And yes, teach your daughter (is she older or younger?)... to TELL HIM to stop it and push him away and to TELL you. I have a daughter, and I teach her to "defend" herself with her brother. Whether it is this or with them fighting. Your daughter needs to know, she can speak up and do something to make her brother stop it, on her. Or if anyone does that to her.
Then, just hope that he does not do this in Preschool, if he is attending a Preschool or Daycare. The other parents would not like it, being done to their kids or to the toys in the classroom.
Your son, is probably doing it, as a relaxing thing. Or as you said, before he falls asleep.
At this age, its not like a child has complete impulse control. But, since your son is doing it all over the place, then you need to try and contain it. Does he do this in public too? Or with other people in the room? Or at other people's homes?
Hopefully this phase, will not last too long.
Or ask your Pediatrician.