She if there is abuse physical verbal then you can file a domestic violence and 498a criminal case with Mahila police station on your husband,
You donot need to send any notice just leave house go to maternal home and you can file a divorce and case there also.
Firstly ask you husband if he agrees for mutual divorce and agree to give you custody of children and maintenance.
Secondly if he doesnot agree file a police complaint upon husband for cruelty and along with that file a divorce petition in the family court. Also file an application for maintenance for you and your kids in the court.
Also you can make an application for custody of children under same divorce petition the court shall grant you custody as for son age 4 child below 5 are generally with mother and same way you can claim for second son as husband is abusive and bad effect on children.
Since in the custody the welfare of child is utmost priority so you shall get the custody.