Night emissions, also called nocturnal emissions, are basically when males have an orgasm during their sleep. They ejaculate usually as a result of a sexy dream. This usually occurs in puberty and late adolescence. It can happen at any time though. It is normal and natural and it isn't a sin because you have no control over it.
Vaginal tightness is a function of many things.
The vagina is a muscle, and like any muscle, it can be strengthened through exercise, like Kegel exercise, which is where you squeeze and relax the muscles of the pelvic area as if a woman was starting and stopping the flow of urine. If you do them regularly, a few times a day, that will strengthen the vaginal muscles. The vagina is very flexible. Most men probably can't tell the difference from one vagina to the next just from their penis. Another thing that affects this is the level of sexual arousal.