“The Brothers Johnson” has a sortorder of “Brothers Johnson, The” – which seems wrong-ish? I think a case can be made for changing this to “Johnson, Brothers, The”.
Maybe English language examples weren’t such a help…
I was taught that names are sorted “last, first” only when both the first and last names are present. That’s why “The Brothers Johnson” is sorted as “Brothers Johnson, The.” I can’t speak to the conventions for the same situation in Spanish, though.
It’d be nice if Guideline 2a. Name of a person in a group artist name at Style / Artist / Sort Name - MusicBrainz included some examples including only a surname, and also of the form “The Brothers <Surname>”.
Looking through https://musicbrainz.org/search?query=“the+brothers”&type=artist&method=indexed&page=1 (especially the second page), it looks like the form “Brothers <Surname>, The” is consistently used for the sort name – I don’t think I see any artists where the surname comes first. (Aside: why are there a zillion bands named “The Brothers <Surname>” but seemingly zero named “The Sisters <Surname>”?)
It does seem unfortunate to be using the same rules for Spanish here, though.
In English, the “normal” approach is to put the surname first (e.g. “The Isley Brothers”), which sorts nicely (“Isley Brothers, The”). Putting the surname last (e.g. “The Brothers Grimm”) seems like it’s either a deliberate, stylistic choice or a result of an already-popular name being translated from another language (“Brüder Grimm”). See also discussions on english.stackexchange.com and forum.wordreference.com.
But in Spanish, with a “normal” noun-adjective order like “Los Hermanos Diaz”, all of these artists will end up grouped together under “Hermanos”.
I tried looking at some lists on Wikipedia but didn’t find anything conclusive (but I also don’t think I saw any examples of sorting these names by surname):
I don’t think I was ever “taught” sortorders; I just picked it up over time, and there is a fair amount of variability with it – especially when trying to mix languages, as Musicbrainz does.
The sense I get (which could be wrong) is that sortorder should generally proceed from most significant to least significant bit. So, for “The Brothers Johnson” – assuredly “the” is the least significant bit, and “Johnson” is most significant?
Likewise for one of OP’s examples – “Los Hermanos Rosario”. If I naively drop that into Google Translate it comes back “The Rosario Brothers”, thereby implying that a sort order of “Rosario, Hermanos, Los” is appropriate. But I suspect most would sort it as “Hermanos Rosario, Los” or without any concern for language as just as is, in the “L” section.
Just thinking out loud here, not intending to make any proclamation or policy…