First, if they're eating meat in front of me, or preparing it in front of me and trying to tell me about my diet, I tell them (VERY POLITELY) that I don't discuss my food choices when people are eating or preparing animals to be eaten. I tell them that I've found people tend to feel overly defensive about it and communications for both sides is hard, so I opt to talk about it after people have eaten.
When they bring a subject to me, it depends on how I'm feeling. If I'm tired, or fed up, or can tell they're doing it just to be a pain and not out of any concern for me, I nod and say "Mmmm, very interesting, I'll look into that".
If I've got the energy (which obviously I never have because where do I even get my protein?!) I try and answer their questions or assertions as best I can. I figure that if someone is engaging me and disagreeing with me, then they're defensive and if they're defensive it means my choices are getting through to them. So, my answering their questions might give them the impetus later on, to do more thorough research or to really question their own assertions.
Now that I'm veg, I can look back at the veg*ns/people who were struggling with the ethics of being omni in my life and the choices they'd made while they were around me. None of them made me go veg, but all of them made me question and absolutely all of them made me defensive. I said some pretty insensitive things in that time, but it was out of fear, more than anything else.
So have hope
(And I hope your situation improves)