Fair enough.
Realistically Nyx probably didn't have her mind made up on who the husband was going to be, it could've still be Mr Monroe (as most of us expected at the time) when Brooke called them "the Monroe family", now that it's established that neither mom or dad (the one that is present and accounted for) uses that name, it feels a little weird.
what if... its Navarro Monroe but he goes by Navarro to 1st hide the girls
(he had 2 dangerous dogs to protect his family so we know its always on his mind)
and 2nd one because that gives him a niche market to work on...
its like although not as excessive as black sports dudes preferring managers who "share" their experience!
ofc that would mean his mother was an Anglo but the father a Latino and he was named under the Latin framework
since the Spanish specific naming rules he could go with naming the girls after his patrilinear name
and using the matrimonial name for business since its the common in Spanish countries!
since the game is in English we assumed a Germanic naming principle
but if you use the southern European naming mechanism,
mainly the Iberian you use the mothers and fathers family name!
if you go by Portuguese rules your family name is the patrilineal
if you use the Spanish rules your mothers becomes the family name!
but both have both parents name as family name...
the difference is the one that gets passed on to the grandkids!
That is new for me, Our name giving system, is similar or same as in Spain.
If you have a couple, He goes by the surname Martinez Rodriguez , and she goes by Fernandez Molina, and they marry,
his name will be Pepe Martinez Rodriguez, and her name , Pepita Fernandez Molina de Martinez, which is used to show that Pepita is married to someone named Martinez. Loosing her Mothers name, hence "Molina" is striked out.
If they have a child, the childs name will be Pancho, Martinez Fernandez; the only way that the child carrys it's mothers name is when the father does not recognize it as his child.
so i assume south american?
anyway unlike the Germanic culture were only the fathers name is passed on in Latin culture 2 family names must be passed!
so he can technically give his daughters a "Germanic" family name while still using a Latin family name to conduct business!
we know he worked with Gabi as a manager, he worked with ZO as a manager probably both Hispanics so using his latin name can be his edge into getting clients to manage!
ok time to explain a few things, both in German an french upon marriage women can keep their names either as "originally" (geboren) which is the typical for Germans
or wife of as is typical for dutch and french e/v or epouse!
i recognize i miss used Latin here since it seems mainly an Hispanic name usage and depending on which part of Hispania it can be mother + father (Portugal)
or in accordance to your example both family names from either the father or the mother, if the family´s are well renown perhaps even more family names!
which can then be gifted wholesale or in parts to the children, mainly if culturally transitioning from a Latin/Hispanic to a Germanic culture!
furthermore Navarro seems to be from a well off family who can afford tens of thousands for an abortion,
so probably some claim to nobility so up to 5 family names to pick from!
thus the reason how the mother can have one name the father "several" but only using 1 or 2 family names for business reasons and the girls
one Germanic name gifted from the father while withdrawing the rest of the family names to grant them cultural assimilation into a new society!
do notice the girls do not speak Spanish, it can even be the fact that Santiago doesn´t speak it either and only the Abuelos speak Spanish in an English speaking country!
but thats just an attempt for me to make sense of the issues,
the mother keeping her name is nothing special
the daughters not having the parents family name is a major issue!
So yes they can be Santiago de Navarro Monroe e castilla mas nombres, daughters!