Ecclesiastes 4:9-12 ASV

Two are better than one because they share the work, they help each other, they keep each other warm, and they protect each other.
The most significant advantages of two rather than one in parenting would be the moral, physical and psychological support to each other.
The importance of a strong marriage to children I believe are the examples of love, support and comfort shown toward each other.
Sometimes one parent may be tired, sick, unmotivated, or morally challenged and needing the other to carry on the duties of parenting children.
I believe the two have a great relationship in these verses.
I believe it is important for the couple to have a common faith. To know and understand where they have been, who they are and where they are going.
I believe it is important for spouses to be close friends.
Todays marriages can be overpowered by financial trouble, infidelity, sickness and disease, addictions and violence. Through love, understanding and support toward each other these troubles can be overcome.
Loyalty to each other inside and outside the family can be shown through the respect of each others boundaries, strengths and commitments.
Through applying Gods examples of how to live in our married lives we can grow stronger together as one and therefore show our children how they can also live there lives. A strong marriage is a gift to both you and your children.
A three corded rope is referring to husband-wife-God which is not easily broken.