Family is indeed a model of the church, called Church Domestic. Matthew 18:20 does not necessarily refer to a family, rather, it speaks of any three Christians, and by extension of any number of Christians. The Church as an institution originally consisted of a small circle of apostles and disciples not related by family, and it established dogmas and had sacraments. That a certain Catholic culture, with statues and rosary beads grew out of it merely shows that Christ founded a living Church where the Holy Spirit abides, not a dead one.
And the Lord gave the Church the Koran and the Book of Mormon...And the Lord lives in a black rock over in Mecca...
Their tradition is just as good and legitimate as the Catholic tradition...Why should anyone believe you and not them???