Basically fight all your natural INTP instincts, and you'll be just fine.
Seriously. Channel what semblance of inner extrovert you have. When you feel like hiding away, stick it out. Even for a few minutes, stick it out with the family. Ask questions, especially the kind that they can answer about themselves or their lives. People LOVE talking about themselves. Give them an inch and they'll take a mile.
And when it comes to helping, offer. I do it all the time, and more often than not you'll be told 'that's okay'. Not all the time, but often enough to justify just asking the 5 simple words 'do you need some help'. And always say 'thank you' when you have the opportunity. Like when someone does something for you, little or small. When meals are over, say how great you thought it tasted and thank whoever made it (how to make sound something sincere 101 - add meaning to you thanks. Don't just say 'thanks', say something like 'that casserole was delicious. Thanks for making it'. Adding a personal touch makes such 'thank you's' sound more authentic). Hell, you don't even have to like it as much as you let on. These extroverted types thrive on attention. They like to feel accomplished and, more importantly, noticed. They love being acknowledged for their work. The more you notice without infringing on their privacy, the happier they are.
I rarely have issues with extroverts because I basically shove aside all natural instincts to retreat into my shell when the time comes. Because, really, in the long run, it pays off to be a little uncomfortable for a few minutes, hours, or even days, than it is to give someone the wrong impression because you couldn't be bothered to adapt for them for a little while (yes, the double standard that you have to be more like them but they don't try to understand you is very frustrating - I hate how I still have to hug people upon saying hi/bye, for example, but a few seconds of discomfort beats many years, if not a lifetime, of awkwardness. Just never forget that there is an end time, that sooner or later you'll have your alone time). You don't have to make conversation with them, but at least invest in making an effort to keep conversation flowing with them should they be the ones to start it. They'll appreciate it, and the result will be beneficial to you in the sense they'll like you more. So, win-win really.
Also, if you've ever worked in a minimum wage customer service type job, you know how you're basically trained to be perpetually polite to even the most assholes of individuals? That sort of experience can REALLY help in these types of extrovert-related situations. Being polite to someone's family or friends is kind of like dealing with stupid customers at a fast food joint. Smile, nod, engage in friendly banter if the other individual starts something, and continue to say please and thank you in a pleasant tone. It does wonders.