It's difficult to do in few words, but I think the best way is to very gently show them where they're wrong — specifically focusing on Jesus. I've done this on two different occasions and they didn't return. This way you (1) get your house flagged as a place they don't want to visit, and (2) you may evangelise to the person visiting you, even if it's just planting a seed.
Here's what I did:
I asked them to read Joel 2:32:
"And it shall come to pass that everyone who calls on the name of the
LORD (YHWH) shall be saved. ..."
Then I asked them to read Romans 10:9-13:
"If you confess with your mouth that Jesus is
Lord and believe in your heart that God raised Him from the dead, you will be saved. For with the heart one believes and is justified, and with the mouth one confesses and is saved. For the Scripture says, “Everyone who believes in
Him will not be put to shame.” For there is no distinction between Jew and Greek;
for the same Lord is Lord of all, bestowing
His riches on all who call on
Him. For
'everyone who calls on the name of the Lord will be saved.'"
Then I emphasised two things:
- The "Lord" that Paul is talking about is Jesus.
- Paul applies Joel 2:32 to Jesus, so he is calling Jesus YHWH.
Finally, I very briefly showed them some early church writings where Jesus is explicitly called God, so that, not only is Jesus called YHWH in the Bible, He is also called God by the generation following the NT era.
We can rejoice in that we have Scriptures and history on our side, and it took me some 5 minutes to illustrate. I figured a few minutes was worth sparing, if it means signalling that I'm not compelled by their doctrines, and more importantly, to tell them the good news of Jesus.