Since it's your husband's family I would follow his lead on how to react to offensive comments they make. Why doesn't he challenge them for racist sh*t they say or do? Has he tried and learned that it's just a lost cause? If so then there are ways you can challenge their beliefs without arguing or getting heated- if you think you are capable of discussing the subject without losing your cool. Like if someone says something racist ask them why they would say or think that. Instead of being confrontational try to ask it as though you are genuinely curious. Listen to what they have to say and you can respond by saying something like, "Really? That hasn't been my experience at all. I think..." and state your opinion- again, not in a way that you're angry with them or trying to challenge them- just that they have stated their belief and you're stating yours as though you find it fascinating that you have such different perspectives. If anyone gets defensive you can back off and change the subject saying that you didn't mean to upset anyone- but you've still gotten your point of view out there.
Approaching someone in a confrontational way usually gets you nowhere because instead of making the other person think you're just making them feel attacked so they fight back. But if you come at it from a place of friendly curiosity then maybe- JUST maybe- it will sort of force them to stop and think about why they hold such feelings that are usually completely illogical. Or maybe they'll see that something they've said is racist when it might never have occurred to them. All of that is a very Pollyanna way to envision the outcome but you never know. Even if it doesn't make anyone think or change their opinion in the slightest YOU will have made it known that you disagree- hopefully without causing a fight.

Change the subject!
My (on again) boyfriend was over yesterday, when DD16 brought over a friend. Introduced them, blah, blah. I'm white, DD is Amerasian, boyfriend is Mexican, DD's friend is African American.
Boyfriend left, so I was having a conversation with DD's friend about the middle school he used to attend, which has since been closed down and re-opened as a charter school serving a largely hispanic population. The kid used the term "beaner".
I could have said, "Uh, did you get a gander at my boyfriend?", but I just changed the subject. To something that I found to be more comfortable.
This is a polite survival tactic (which is what you're looking for, I'm guessing). How 'bout them (fill in sports team here)? Wow, I sure love your (fill in clothing or furniture item here), where did you get it? My, the weather sure is (adjective)! What do you think about the whole (celebrity name) scandal?

And...try to think of the entire visit as an anthropological study. Don't judge, just observe, and you can report your findings here on hipmama.com!

www.myspace.com/placentamusic

I have learned that, for myself, responding to offensive comments just gets me riled up and does absolutely nothing to affect any opinions in the offending party. (For example when I reacted to an offensive comment from my Grandpa about American Indians in a western movie by yelling: "maybe that poor little white girl is a small price to pay for having stolen their land and exterminated their ancestors". I was 12 and everyone laughed.)
Now I tend to avoid confronting bigotry unless 1)there is a child who is witness to the bigotry or 2) there is someone who does not feel comfortable defending themselves or those they love against offensive comments and I can back them up.
Most of the time I'm able to avoid bigots or they know me well enough by now not to get me started.
You may want to talk with the 8 year old beforehand about tolerance and how some people don't share your same views, etc.

I have to deal with this a lot with extended family and I was discussing with a friend of mine how to strike the balance between sticking to your radical ideals yet not piss off family, who you may love, just tolerate, or don't want to alienate. Mostly it depends on the demeanor and personality of the people you're dealing with. For example, My MIL is super conservative and confrontational but doesn't take things personally so I argue back with her when she says horrible/offensive things, taking cues from the way my SO interacts with her. on the other hand, SO's sister is conservative but mostly really nice and I want to stay on good terms with her. When/if she says anything offensive I ask that we change the subject. Say, "I disagree and I don't want to argue with you, let's talk about something else." Usually she agrees because she cares about social niceties, which MIL does not.

I would take into account the person that you're talking to. also have a conversation with your SO about what kind of relationship he wants to have with these people and how he would like to interact with them. It's his family and he's the one who has to deal with them most of the time.

"revolution is not a one time event" Audre Lorde