It's probably a good idea to put some distance between your inlaws and both you and your husband. Even though you've had a significant amount of time "together" prior to your wedding, I'm guessing that the JW inlaws had hopes that you would convert to the JWs and that their son would return to The Truth™.
Frankly, the way they treat you like second class citizens, if it ever comes up in conversation with them why you never showed an interest in their religion, I would flat out tell them "Why on earth would I want to associate with a religion that treats people as badly as you've treated [hubby] and me?" Make a list of specific events and their behaviour, keep it handy because you never know when you'll have the opportunity to address this with them. Then establish some boundaries with them and do not let them cross your boundaries. This will become increasingly important if you are going to start a family - you do not want your inlaws to have unrestricted access to children where they will have the opportunity to indoctrinate them with JW beliefs, including such beliefs that you and your husband are "following Satan" or that you are "making Jehovah sad" or that you will all be "destroyed at Armageddon" because you "don't love Jehovah". Your children do not need to be terrorized like that.
Also, I would start making a plan with your husband to sell his part of the business to his brother (talk to a lawyer first to be sure that your BIL isn't going to take advantage of your husband) and find work that doesn't involve his family. If they treat him like crap at work, it's just an extension of how they treat you both in person. Neither of you are required to tolerate that kind of psychological abuse. He deserves to be respected in the workplace just like any other employee or partner in a business relationship. He's not required to seek their approval - if he's close to 30 years of age, as I gather from your post, if he hasn't got his family's respect by now, it ain't ever gonna happen. It's time to cut your losses and move on to friendships and relationships (personal and business) where you are respected for who you are, not for the religion you belong to or not.