Depending on how you define "artificial family construction", I think that the ship probably sailed on that issue when divorce became common.
By this I mean the production of children outside of a marital context- a single woman impregnating herself through a sperm donor, a gay couple becoming pregnant through insemination- models of family which deliberately set out to exclude either a mother or a father from primary participation in the child's life and treat one parent as a "donor".
But even in a Catholic context, marriage does not necessarily imply anything sacramental. Take me: I was married in a Catholic church, but the priest made it clear that the marriage would not be a sacrament for me as it would be for my wife because I was unbaptized.
Also, would the Catholic Church consider homosexual marriage to carry no weight if, say, a Catholic couple went to be married in the Church and one of the prospective spouses disclosed that he or she had previously been married to a member of the same sex?
That is correct, a homosexual marriage would carry no weight because, in the Catholic meaning of the term, homosexual marriage is not possible.
I think the Catholic problem is that it rightfully sees marriage as historically serving as a fundamental institution for society- the building block of society as it were. Marriage for a great portion of human history has not been principally about love, but about social utility [ and necessarily so for that time!]. This is where the difficulty is introduced.
Catholic doctrine and its current evaluation of the natural law continues to see marriage as more than an individual affair- it necessarily involves the interests of the whole society, and so as much as it is geared towards the union of two persons in love, it is also geared towards the raising and formation of the future generation. Insofar as this is true, I will always maintain a
heterosexual priority in my theological/ philosophical understanding. This is because heterosexual unions are the fountain of biological life and the primary sphere for the development and nurture of children. I think it is quite reasonable to understand homosexual unions to play here a kind of
supporting role in the duty towards the formation and rearing of future generations. Though this does imply a kind of subordination or a kind of
technical inequality that people really oppose, and which they try to correct trough technological means (such as artificially creating the conditions of heterosexual fecundity through insemination). Though I do not think it has to mean that there is less dignity involved in one union than another- but certainly a difference in their place or role as integral to the structure of society. Strictly speaking, what I am saying is that we need to find a place in the "body of society" for homosexual unions. It could not, in my understanding, be functionally equal to heterosexual unions- my toes are not equal to my fingers, but chop them off and I lose my balance.
Catholic teaching attempts to maintain the broader societal aspect of marriage, while at the same time [today] trying to develop a [very modern] theology of love that means marriage is not merely a pragmatic affair, not simply done with a view to the whole, but also something personally authenticating and enriching and freely done.
In principle, I agree with this, but I see it as really a first attempt among, perhaps, several as the meaning and utility [and deficiency] of marriage in a modern society becomes clearer.