I would question them constantly on the issue of justification.
It's a big word I know. All it means is "how we get our sins forgiven."
Read Matthew 26: 27 & 28 from the NWT :
As they continued eating, Jesus took a loaf, and after saying a blessing, he broke it, and giving it to the disciples, he said: “Take, eat. This means my body.” And taking a cup, he offered thanks and gave it to them, saying: “Drink out of it, all of you, for this means my ‘blood of the covenant,’ which is to be poured out in behalf of many for forgiveness of sins.
Tell them that you want to be shown from the New Testament how a person can get their sins forgiven OUTSIDE of the New Covenant. Assure them that once they can show you that scripture you'll be happy to get baptized.
When they start demanding that they ARE part of the New Covenant, even though they officially and very publicly show that they ARE NOT part of the NC each Memorial, ask to see a scriptural reference to people getting saved from judgment that reject the emblems.
When they cannot; remind them that the doctrines instituted by Jesus and the apostles cannot be changed without incurring a curse:
But though we, or an angel from heaven, preach any other gospel unto you than that which we have preached unto you, let him be accursed. - Gal. 1: 8
Remind them that it is they that taught you to revere the scriptures and that your questions are sincere. You REALLY do not want to be judged by God for your sins.
Read up on the Reformation and how the issue of whether or not a person's church can save them was settled 500 years ago.
My website has some other info along these lines here. But keep it simple. Don't allow them to drag you into any other topic! Let this be your motto:
For I determined not to know any thing among you, save Jesus Christ, and him crucified. 1 Cor. 2:2