Rather than dispute with the JWs, I suggest putting a big, welcoming smile on your face, opening your door as wide as possible, and saying to the uninvited visitors: "O, I'm so glad you're here; please come in! I'm about to take a rare roast beef out of the oven and I'll be happy to share it with you - we'll say a little prayer together, have our nice dinner, and then have some lovely fresh-brewed Blue Mountain Coffee!"
Actually, JWs do drink coffee. (It's Mormons who abstain from coffee.) They might turn down an offer of coffee, however, as they usually want to focus on their mission. Even though JWs don't eat blood sausages, they wouldn't have a spiritual objection to a rare roast beef. In their view, once an animal is bled out in the slaughtering process it is permissible to eat whatever blood is left over in the muscle meat.
Now, JWs will want to avoid praying together. They believe the God they worship is not the same as ours. In fact, they believe our religion is from the Devil and that is who we are actually worshipping.
