I don't agree with the lifestyle at all, but yes, they should be allowed to attend church. As long as they aren't doing things like hugging, holding hands, kissing and whatever during service, and as long as they can listen to truth without interrupting...then why shouldn't they be allowed to attend church? Where else are they going to hear the word of God?
I'm not saying puff 'em up and tell them that it's ok to live that lifestyle, but preach the true word of God to them!