It would depend entirely on the attitude / behavior of the same-sex couple when they are in the congregation. If they are listening like everyone else, fine. If they appear to be attending just to cause turmoil -- I would probably have a deacon with me and invite them over for lunch -- see what their reaction is.
If you are speaking as a pastor of a church -- then you Do have the responsibility of protecting your flock from obvious sinful behavior.
And, yes, their relationship to God through Jesus Christ would be the most important. Sit down with the same-sex couple and approach their salvation -- share Your testimony with them and invite them to do the same.
There's a fine line here. Attitude / appearance makes the difference.
I don’t think anyone should be making out in the church pews, regardless if your homosexual or heterosexual. There is a time and place for everything, and that sort of behavior is meant for the bedroom, and I would make sure that the couple is made aware of that.
And I agree, the attitude/appearance of the Christian church could either push these people closer to God by showing them a taste of Gods love, or away from God by showing them their intolerance.