Dear Sean:

Before answering your question, one correction: Your friends are not "Eucharistic ministers," they are Extraordinary Ministers of Holy Communion. A priest is a Eucharistic Minister.

If these friends do not believe in the necessity of the Sacrament of Confession, and thus do not avail themselves of the Sacrament, then they are not in communion with the Church and are committing a sacrilege each time they receive the Eucharist. They are also risking their souls to hell.

Under no circumstances should they be Extraordinary Ministers. The parish pastor should be notified of this situation unless the couple resigns their participation as Extraordinary Ministers, or come to accept Church teaching on this subject.

The statements in the Catechism are sufficient for any Catholic who is not an arrogantly playing Pope. The Catechism quotes canon law and several Church documents and Saints. The I have added the some of the footnotes in green to the following quote that include other Church documents and the Bible:

The confession of sins

1455 The confession (or disclosure) of sins, even from a simply human point of view, frees us and facilitates our reconciliation with others. Through such an admission man looks squarely at the sins he is guilty of, takes responsibility for them, and thereby opens himself again to God and to the communion of the Church in order to make a new future possible.

1456 Confession to a priest is an essential part of the sacrament of Penance: "All mortal sins of which penitents after a diligent self-examination are conscious must be recounted by them in confession, even if they are most secret and have been committed against the last two precepts of the Decalogue; for these sins sometimes wound the soul more grievously and are more dangerous than those which are committed openly." (Council of Trent (1551); DS 1680; cf. Ex 20:17; Mt. 5:28)

When Christ's faithful strive to confess all the sins that they can remember, they undoubtedly place all of them before the divine mercy for pardon. But those who fail to do so and knowingly withhold some, place nothing before the divine goodness for remission through the mediation of the priest, "for if the sick person is too ashamed to show his wound to the doctor, the medicine cannot heal what it does not know." (Council of Trent (1551), DS 1680; cf. St. Jerome, In Eccl. 10, 11)

1457 According to the Church's command, "after having attained the age of discretion, each of the faithful is bound by an obligation faithfully to confess serious sins at least once a year." (Cf. Canon Law 989; Council of Trent (1551, DS 1683; DS 1708) Anyone who is aware of having committed a mortal sin must not receive Holy Communion, even if he experiences deep contrition, without having first received sacramental absolution, unless he has a grave reason for receiving Communion and there is no possibility of going to confession. (cf. Council of Trent (1551, DS 1647, Canon Law 916) Children must go to the sacrament of Penance before receiving Holy Communion for the first time. (Canon Law 914) 

The affirmation of the Council of Trent and Canon Law merely repeats the continuing teaching of the Church since the first century.

Confession is also mentioned in the Bible:

Mt 9:2-8 establishes that the Son of Man has the authority to forgive sins

John 20:23 establishes that Jesus delegated his authority to his priests when he told them that the sins they forgive/retain will be forgiven/retained

Mt 18:18 also establishes this delegation of authority when Jesus gave the power to bind and loose

John 20:22 shows us that this delegation of verse 23 is to his priests who were "ordained" in verse 22

James 5:13-15 specifically says that the prayers of the priest forgives sin. This is not the rank and file Christian, this is the priest (in Greek, presbyters)

James 5:16 commands us to confess

1 John 5:16 affirms that there is such a thing as mortal (deadly) sin.

We must come to God through the Church and her Sacraments initially (baptism/confirmation). When we commit a mortal sin we have severed that relationship with God and His Church. Since we have severed that relationship that is brought to us by the Sacraments, it is the Sacraments that must restore us to God and His Church. The Sacraments of Baptism and Confirmation can only be conferred once. Thus the Sacrament of Confession is the Sacrament that can be repeated as often as necessary to restore us to fellowship with the God and His Church.

Venial sins do not require the Sacrament of Confession because Venial Sins do not severe our relationship with God and His Church, it only bruises it. Those bruises are healed by ordinary means such as doing good works, prayers, and receiving the Eucharist. But then we severe our relationship with mortal sin, only the Sacrament of Confession can restore that.

A good article on this is Forgiveness of Sins and also Confession. This last article includes many quotes from the Church Fathers.

The teaching of the Church on the necessity of the Sacrament of Confession when one has committed a mortal sin is clear and unambiguous. Only a fool would think Confession is not needed. Such a person is certainly not in communion with the Church.

We will pray for them.

God Bless,
Bro. Ignatius Mary