As far I understand, the divorce papers are to be signed by 2 people. If you refuse to sign it than nobody can force you to get divorced. By sending papers your husband can't get a divorce.
I think you should make a police complaint that your husband and mother-in-law used to torcher and beat you thats the reason you were forced to leave the home. I would not advice you to ever go back to that house where people don't treat you with respect.
one piece of advise to every girls, don't marry those guys who live with there parents..as sooner or later there you are going to run into issues with in-laws. Also don't get pregnant without 100% surety that the guy is right for you or not.
It is better to live alone than with somebody who left you alone when you needed him the most during you pregnancy.
I am sure someday you will find someone who will truely fall in love with you, marry and treat you with respect. And that day nothing else will matter.