That's a very good question. I'm not a Mormon so I guess I wouldn't be the right person to answer this, but as a Christian I can give my personal advice. 
 
I have in-laws exactly like this, and the only thing you can do is turn the other cheek, treat them as respectively as you would want them to treat you, and don't give in to their bullying.  
 
I know it seems hard and you wish you could just fix everything, but this is not the kind of reasoning that would lead someone to church. You could confront them perhaps, tell them exactly how you feel and that you wish they'd just be nice to you. 
 
Hope this helps.

It seems you have experienced how the church can be perfect but the people who go to the church are not perfect! That's why we go.  
Your in-laws may be feeling hurt and taking it out on you. Not the right way to act but it is happening just the same. It sounds like you know alot about the church so I am sure you know that we believe that families can be together forever. They want this blessing for every single one of their children and see that you and their son will be parted at death not to have eternal happiness together. Their actions are not right but maybe it will help you to see why they are acting that way. It is right for you not to convert if you do not believe the truths of the church. You must do it for yourself not for family or to make someone happy. Maybe your hubby could remind them of the love of christ and how much you would like to be with the family and not always feel like they are pushing. Remind them that they taught him well and now it is his time to make his own choices, just like heavenly father has done with all of his children, they need to love you, support you and hope and pray that your choices will lead you back to our heavenly father. Because isn't that what we are all here to do? I do not believe that Heavenly Father wants to save just some of his children. He wants us all to return to him. And loving and being supportive is how we can all hopefully make it back to him.