How do we answer the church if I and my fiancÚ are asked if we have had sex before marriage when we have engaged in foreplay of sexual activities? Knowing we cannot be wed in the church if we say yes, though we didn't do the real act.
First, there is no requirement in the Bible for weddings to be done in a church building or sanctioned by a church. God requires people to be married before having sex and establishing a new family. The details of how that marriage is to take place is purposely left vague. Paul stated that people who are married before becoming a Christian are still married after one or both become a Christian. "For the unbelieving husband is sanctified by the wife, and the unbelieving wife is sanctified by the husband; otherwise your children would be unclean, but now they are holy" (I Corinthians 7:14).
There are basic requirements for a marriage, which can be found in Marriage Covenants. But suffice it to say that even if you are married at the courthouse, you will be just as much married as when a preacher performs the wedding.
What you and your fiance did was sinful. Paul stated, "Now concerning the things of which you wrote to me: It is good for a man not to touch a woman" (I Corinthians 7:1). That sin needs to be dealt with. Both of you need to recognize that it was wrong and commit yourselves to not repeating the sin (II Corinthians 7:10-11). You also need to go before God to ask for forgiveness (I John 1:9).
It is a shame that a church isn't able to recognize that people who have sinned can repent and be forgiven by God. "For if you forgive men their trespasses, your heavenly Father will also forgive you. But if you do not forgive men their trespasses, neither will your Father forgive your trespasses" (Matthew 6:14-15). A church which holds a person's past forgiven sins against him is not a true and faithful church. I would urge you and your fiance to find a church that follows the Bible and not their own whims.
But even so, if this group says that acts of lewdness means you cannot be married on their property, then so be it. Get married elsewhere. Do not lie about your past sins. If they cannot accept your repentance, then that is their problem and not yours.