Is there any relative from the wife side that your on better relationship with? Can try to ask the person as a middle man to help speak words for you. Otherwise, can have a "open talk" with your parent in law including your wife. You can tell them about the stress that you are facing, and what are the things could happen, if you really divorce, you can ask them, are they willing to take care of the grandchild for you and do they want their daughter to be a single mum. Sometimes they are trying to protect their daughter, without knowing that they harm that they have caused.
you must love your wife very much, cos this kind of problem is already forseeable even at the beginning of your relationship. There must be something about her that you love so much that you hang on till now. Wouldn't it be such a waste to give up? Esp your wife is giving birth soon, if dont handle well, she may have depression. And your wife's brother, maybe can ask him to help put in some good words for you.
My parent in law also dont really like me, but lucky for me that they are in Msia at the moment. Tho I heard they may have plans to come stay with us "permanently" maybe in a few yrs time. No matter how hard I tried, I cannot win their love, so I tried to give them more pocket money then the rest of their daughter in laws. They still dont like me and my daughter, but at least they try to stay out of my way now.
PS : I suspect they dislike me becos I am a Singaporean , they always hope their son will marry a Malaysian and return there one day for good. My parent in law got 4 sons 2 daughters.