Good for you for nursing your baby, even among critics or less than supportive family.
A few ideas:
Next time you're invited to said family member's home, have a talk with them about how you expect to be treated before arriving, whatever that means for you and be kind but firm. If they agree to your terms and behave differently upon your arrival, feed your baby and then leave. If they aren't able to support your decisions, it may affect you emotionally and in turn affect your intentions of a long and healthy nursing relationship with your little one. I think if you make it clear you're unwilling to be treated like an outcast, that they'll treat you more kindly and gently than they are now.
Rally your husband's support. He may be unaware of how this is affecting you/bothering you. Is he? Express to him how important his support is for a successful time breastfeeding and especially in public. Of course, you can speak for yourself, but it's always powerful when someone else speak's on another's behalf, man or woman. If your MIL is supportive, rally her support. If anything, it will strengthen your relationship with her. :) You're doing enough work raising a baby and breastfeeding her, not that you don't know. :) But taking criticism from anyone, especially family makes being a new mom less than the joy it really should be.
If the men really are uncomfortable (which my guess is that it's truly the women) then the bigger problem is not you NIP, but their inability to control whatever arousal is occurring from a mother doing the most natural thing she can for her baby. Am I right? There is nothing sexual about breastfeeding. Our culture over-sexualizes everything. So if someone else only sees the fact that you're exposing yourself minimally and they can't see the heart and extreme care you're taking in nourishing your baby, then they've been overly influenced by culture's mindset that a woman's breasts are for sex and that is not all they're intended for...at all. :) So bare that in mind and if you're comfortable with it, share that sentiment with your family. It's not your fault and you (nor any BF woman) should be penalized for culture's wrong doing. I know we are, but we shouldn't be.
Lastly, cover ups never worked for me, not at a few weeks old and not now as my toddler is 22 months. haha I did invest in a few BOOB brand nursing tops though. Have you heard of them? If not, google BOOB brand nursing tops. You can find them at a variety of online retailers, other than boob. Naturalmomgear.com is where I bought mine because they're more affordable there for some reason. I also bought some on ebay for super cheap! They're an easy open design, very modest, and the only brand I wear because they're really practical and don't feel like nursing clothing. It makes nursing discreetly a breeze without making you feel like you're living 2-3 layers. Instead, they're an envelope-like design, which sounds weird, but check them out. Even if you only invest in a couple, that would be helpful for when you visit with family.
Oh, and truly, I think your family should be making the drive to you! You have the new baby after all. This way they're on your turf, meaning your rules or the highway. And, if mr. uncle father brother in law is uncomfortable with you nursing, he doesn't have to come. :)
Best of luck. I hope things improve. :)