I had an interesting discussion with a friend recently. On the topic of Jehovah's Witnesses, he explained that he'd been told the best way to "deal with them" is when they come to your door, invite them in and make them a drink. The reasoning? These people have been told by their leaders "If the world hates you, you know that it has hated me before it hated you. If you were part of the world, the world would be fond of what is its own. Now because you are no part of the world, but I have chosen you out of the world, for this reason the world hates you." (John 15:18-19, NWT). So, when they receive the hatred they do from the world, what do they think? When even Christians slam doors in their faces, well, obviously, Christians are of the world, so they hate us, because Jesus chose us. So obviously, when Christians show them the love of Christ, a chain is broken.
But wait, doesn't John exhort us "If anyone comes to you and does not bring this doctrine, do not receive him into your house nor greet him; for he who greets him shares in his evil deeds"? (2 John 1:10-11). Well, actually, no. He wrote this to "...the elect lady and her children..." (v1). This is quite important, as there are things in Scripture addressed entirely to the primary audience. Paul, for example, has not been hindered by Satan in his attempts to come to our churches (1 Thessalonians 2:18). Neither are we expected to "Greet the brethren who are in Laodicea, and Nymphas and the church that is in his house." (Colossians 4:15). This, of course, does not mean everything in every Epistle should be treated as just personal letters between people we have nothing to do with. It's just vital to remember, we draw principles from Scripture, not always direct and wooden commands. Furthermore, no verse should be taken on its own; the preceding and following verses should always be taken into account, along with any other relevant Scriptures.
So what, in context, is John saying to the elect lady? Well, what I gather from commentaries is that she was actually engaged in a particular ministry of hospitality. She would give aid, even accommodation, to the servants of Christ, greeting them and bidding them God speed. But when it comes to false teachers, we are not to yield to them for even an hour (Galatians 2:4-5). The elect lady, had she given false teachers the same love and respect she gave the brethren, would have shared in their sin, not by trying to bring them to repentance from within her house, but by allowing them to use her hospitality for their own Godlessness. It's not about "don't ever let them in", but effectively, don't let them set up camp, much less a temporary base of operations.
In the book of Galatians, Paul actually exemplifies the part about not greeting heretics. Notice the sharpness of his greeting to these, who have "become estranged from Christ" and "fallen from grace" by entertaining a works-based "gospel". In every other epistle, no matter the state of the church he is addressing, Paul usually applies some epithet of honor to his recipients. But with the Galatians, it's just "To the churches of Galatia...", followed almost immediately with "I marvel that you are turning away so soon from Him who called you in the grace of Christ, to a different gospel,".
So ultimately, no, there is no sin in having unbelievers enter your house for a Gospel talk. There are two caveats, however. First, you need to know what you're doing. As Paul warns us, "...Satan himself transforms himself into an angel of light. Therefore it is no great thing if his ministers also transform themselves into ministers of righteousness..." (2 Corinthians 11:14-15). False teachers are as sneaky as the devil who binds them, and the ones who come to your door are well trained in dealing with your beliefs. Ensure you, likewise, are knowledgeable in Scripture, and of course allow the Holy Spirit to lead you.
Relating to that, do not allow them to lead, especially if there are others, your children perhaps, observing the discussion. If you allow them to give their view, do it with a cross-examination mindset. Give them a drink, if they'll take it. Give them the Gospel, even if they won't. Pray for them, show them the love of Christ, and if they reject you in the end? Kick the dust from your feet as testimony against them. Your job is to speak, whether they listen or not. God deals with the rest.