Need legal advice

As you are not interested to initiate any legal course of action against your husband or his relatives,  you must know that what legal actions are available to him.  He may file Restitution of Conjugal Rights case against you alleging that you have left matrimonial home without reasonable cause and put some more allegations like you ill-treated his parents, you did cruel acts against him etc. etc. If he is interested in divorce, he may file it.  Further, he may file child custody case.  As you have got valid reasons to leave his companionship and matrimonial home, you can contest RCR / divorce case by engaging a proper advocate.  In child custody case, as the child is only 4 years of age and if he files child custody case, it is more likely that he will get visitation rights but not custody, as in these cases, the court will consider the welfare of child as the dominant factor to decide the case.  More likely you will get the custody of the child.  As you are not inclined to entangle in legal web, you write a simple letter by speed post/registered post to your husband explaining the hardships you met in the matrimonial home forcing you and your child to come to natal home.  Explain the facts threadbare without putting imputations against anyone or otherwise that may provoke him to initiate some legal action, as said above. 

1. He may file S. 9 HMA i.e. plea before court for restitution of conjugal right (seeking court assistance for an order for you to rejoin his company). It is your sweet wish to rejoin if you feel you and child would be safe or not to rejoin him if you have valid reasons and Court cannot fore you for the same i..e if ever he succed in getting one such Order.
2. In husband wife relationship consent of husband before leaving matrimonial home is duty of a wife.
3. If you donot currently want divorce from him then inform your wishes to stay at your native place till things return to normalcy.