I have seen so many couples...even within my own family...worry about not having children. They are so intent on 'making a baby' that they forget that the purpose of (their) love-making is the joint expression of how much they care for each other, from which a new life can result.
Often, there is something 'deep down within' going on that refers to whether a child is really wanted and welcome. Is there a fear of pregnancy, is one or the other ready for parenthood, will a child get in the way of the career, will its parents have time to devote to it, will it be healthy, is it to 'prove' something........and, worst of all, is a child the hope of saving a failing relationship?
If you have undergone fertility tests and both couples are healthy in producing seed and eggs, maybe they should look deeper into themselves for an answer as to why a child is not forthcoming.
I've seen couples 'try' for years to have a child, think it no longer possible, stop worrying about, prepare to adopt, love each other for themselves.....and BINGO!
I hope you are as successful.