Someone said :
If we regulate surrogacy, then there should be no distinction between same-sex and mixed-sex couples.
The real question is whether we should allow surrogacy, and if so, what rules should go with it and how should they be enforced. At one end of a spectrum, permitting commercial surrogacy gives rise to concerns about poorer or vulnerable women being exploited. On the other hand, a complete ban would exclude the possibility (as happened in Ireland recently) of a sister agreeing to be the surrogate, where there clearly was no concern that exploitation was involved.
But in the Irish case you mention, there were serious ethical questions raised about the sister being the birth mother of her niece/nephew.
The adoptive mother should have gone through the adoption process: either be found suitable to adopt the child of (her husband + her sister), in which case happy days; or be unsuitable, in which case the best interest of the child is not to be raised by her...
I tend to agree with the current Irish legislation that the birth mother is always considered to be the mother for all intent and purposes, and that she can only discharge her duties and rights through an adoption process.
As for the father, in case of marriage he is assumed to be the legal father, until proven that he is not the biological father (in some cases).
I must say that I disagree with surrogacy in general.
Especially when it results in creating orphans of [birth] mother on purpose. (Note that orphans are not only bereft of their parents, even if it is the most common usage of the term...)
I totally agree with adoption as a right of existing children to find a stable, loving family. (Adoption is not a "right" of the prospective parents)
Surrogacy is aiming at creating children so as to make them adoptable by someone other than their birth mother.