Broken record and fogging are both amazing tools. I remember a conversation I had with my mother once, the first time I tried it. She kept asking why I wasn't going to the KH any more. I kept saying, "I don't want to discuss it." When she added the JW threats -- you'll die at Armageddon -- I said, "you're probably right, but I don't want to discuss it."
After a while she ran out of ideas, and she never tried again. It helps, too, if you can step back and watch the conversation as if it's a movie, and get some amusement out of their reactions.
Also, it's OK -- especially since it's your house -- to name their behavior. "I can't believe you are trying to make me feel guilty." Or, "guilt doesn't work." Or, "I can't believe you said that." Or, if you've had enough of their behavior and are tired of being nice, "you're a bit manipulative, aren't you?" Or, "don't you think that if we open our house to you and treat you like a guest, that you ought to at least pretend you like us?"
The secret is to lob the guilt or insults back at them, and then refuse to discuss it any more.