Dear Pitsa
I agree with Annie that the two of you need to talk these things through. You may find the article about marrying across faiths here useful. Although your husband shares your faith, his family don't and this is causing difficulies.
I wouldn't have thought that the slap was normal JW behaviour. It sounds more like a woman who likes to control her children even when they have grown up.
Have you considered doing some marriage preparation to help you talk through the issues you face? You could consider an
Engaged Encounter weekend or a
FOCCUS or
Prepare programme. Each of these will give you the opportunity to explore how you can build a strong marriage despite any differences that you may have.
All the best
Kate