Yes there are many many others in sexless marriages for various reasons, some of which are out of the couples control.
To answer your first question, mutual abstinence is not sinful. If you don’t want to have children, it is the most logical and effective way.
This is not an entirely accurate answer, because it does not remind the OP that there ought to be a serious reason to avoid sex when the goal is to avoid pregnancy. NFP is not meant as an aid to help Catholics avoid the blessings God intends for them to have. Children and marital relations are among the essential goods of marriage, and while they can be avoided for legitimate reasons, they are not to be renounced for selfish reasons.
*CCC **The openness to fertility **
1652 "By its very nature the institution of marriage and married love is ordered to the procreation and education of the offspring and it is in them that it finds its crowning glory."162
Children are the supreme gift of marriage and contribute greatly to the good of the parents themselves. God himself said: “It is not good that man should be alone,” and “from the beginning [he] made them male and female”; wishing to associate them in a special way in his own creative work, God blessed man and woman with the words: “Be fruitful and multiply.” Hence, true married love and the whole structure of family life which results from it, without diminishment of the other ends of marriage, are directed to disposing the spouses to cooperate valiantly with the love of the Creator and Savior, who through them will increase and enrich his family from day to day.163
**1653 **The fruitfulness of conjugal love extends to the fruits of the moral, spiritual, and supernatural life that parents hand on to their children by education. Parents are the principal and first educators of their children.164 In this sense the fundamental task of marriage and family is to be at the service of life.165
**1654 *
Spouses to whom God has not granted children can nevertheless have a conjugal life full of meaning, in both human and Christian terms. Their marriage can radiate a fruitfulness of charity, of hospitality, and of sacrifice.
and canon law:
***Can. 1055 §1. **The matrimonial covenant, by which a man and a woman establish between themselves a partnership of the whole of life and which is ordered by its nature to the good of the spouses and the procreation and education of offspring, has been raised by Christ the Lord to the dignity of a sacrament between the baptized.
**Can. 1096 §1. *
For matrimonial consent to exist, the contracting parties must be at least not ignorant that marriage is a permanent partnership between a man and a woman ordered to the procreation of offspring by means of some sexual cooperation.
Having said that, I would not jump to the conclusion that this couple has lost the desire for sexual relations for self-centered reasons, which is to say solely because they do not want to make sacrifices for children they have been granted the means to care for but do not want to care for. That a reluctance to make the sacrifices asked of parents and a prejudice against children is unfortunately in their hearts does not imply it is the only reason they are refraining from marital relations. They may, for instance, want to devote themselves to prayer and a level of service to the Lord that is more typical of that attainable by celibate people. These considerations are a bit beyond the pay grade of a typical layperson to sort out (as opposed to a priest or someone trained and formed according to the Church’s wisdom in pastoral counseling.)
Although the authority to make a decision of this kind rests with me and with my husband, I would not do this while relying solely on our limited ability to discern. This is something that wants on-going spiritual advice from a competent party. If the OP couple wants a Josephite marriage, that is a marriage that abstains from sexual relations for the sake of service to the Lord, they ought to have regular spiritual guidance for their choice. Not just one session, but
regular guidance and
regular inquiries into how they are doing.
In any event, I would strongly recommend that this couple pray regularly about their repugnance for people who haven’t reached a certain age. To carry a prejudice against an entire class of persons is not the attitude of Heaven, but something to work on–
particularly when one has a prejudice against children! They ought to meditate on this passage of Holy Scripture and ask themselves why they are rejected someone that Our Lord specifically called his disciples to welcome as if welcoming the Our Lord Himself as a guest:
He called a child over, placed it in their midst, and said, “Amen, I say to you, unless you turn and become like children, you will not enter the kingdom of heaven. Whoever humbles himself like this child is the greatest in the kingdom of heaven. And whoever receives one child such as this in my name receives me. Whoever causes one of these little ones who believe in me to sin, it would be better for him to have a great millstone hung around his neck and to be drowned in the depths of the sea. Woe to the world because of things that cause sin! Such things must come, but woe to the one through whom they come! … See that you do not despise one of these little ones, for I say to you that their angels in heaven always look upon the face of my heavenly Father." Matt. 18:2-7, 10
The next time the OP couple sees some children, they need to think hard about what the Lord had to say in those passages, and challenge themselves about why they see children so very differently than their Lord and Savior sees them.