Help with in-laws

Hopefully this is considered a "relationship" so I'm posting in the right forum. My husband and I have been married for 5 years and we haven't seen his parents or brother socially in about 4 years. Now a situation has arisen where I feel this impasse must be broken. Maybe for my husband's sake or maybe because I feel guilty, I'm not sure.

The 6 months leading up to our wedding we saw them quite a lot (Friday night cards, church, etc.) but near the wedding they found out my true age (they had assumed I was 10 years younger than I am) and withdrew their consent for the wedding, as did the church (which we both have since walked away from) and slowly stopped seeing any of them for various reasons but the foremost one for me was the stress caused us to argue constantly over how to handle them or why we didn't or couldn't. It just became unbearable. The mother is loud, obnoxious, rude, nosy and has been proven to be a gossip if you give her half a chance. The brother is socially pathetic and as an example of his manners... eats greasy chips and then wipes his hands on my brand new white sofa cushions while my husband says nothing, even after I hand them both napkins and say "You boys need to wipe your hands on napkins, not the furniture!" but the brother did not get the hint and his napkin went unused, much to my disgust (and anger with my husband for not "handling" his own brother!) This was probably 99% behind all of our early arguments as a couple. The stress mounted and we just stopped seeing them because I refused to. His father has been known to verbally admonish his wife by calling out her name on occasion when she's rude, but then she just carries on with her behavior and isn't challenged any further. My husband often closed his eyes and just zoned out leaving me stranded to deal with them essentially alone. I don't fault him for it, he was very young and he's come a long way since, but hasn't been tested in a critical situation yet and I'm nervous. He was the youngest in a very controlling, manipulative and religious family and was never taught to speak out or even speak his mind (or even have a mind) and we're BOTH pretty lousy at speaking up in general or asking for what we need or expect from people, so I am not a great help either. I even answered rude questions because my immediate response around authority figures is to obey. I hate myself afterwards, but it's like a reaction I can't help at the time.

However - we recently bought a quite spectacular new home and I know my husband would enjoy showing it off and possibly part of that is to say "I've thrived with this woman you judged!", who knows. I want him to be able to enjoy showing it off in any case but the closer it comes to the time this actually should go down, the more sick inside I feel knowing I'm willingly subjecting myself to their rude and obnoxious behavior. Hopefully we've all grown up a little bit in the ensuing 4 year period, but if I'm sick to my stomach and shaking when they show up (I am pretty sure I will be) it's going to be really difficult to have a helpful attitude. I don't want to start all over again with the stress and arguments over seeing them and if we open this door a little bit they'll probably get pushy about keeping it open and frankly I just don't enjoy their company that much. They try to be nice, but they haven't been exposed to good manners or something and I just can't abide them. I don't know what to do, I'm really sad about this situation, and I'm certainly not accostomed to willingly subjecting myself to such unpleasantness but I want to do the right thing here. Any advice truly considered and greatly appreciated.

Deedee