The h-prothesis with le
is correct, even with proper names.
The thing about repeated prepositions is kind of a hot topic. If you want to play nice with the prescriptivists and conform to some of the more contemporary thinking about Irish grammar, repeat the preposition. However, I'm inclined to disagree with strict rules about it either way because of the nature of agus
is a very strange word in the Gaelic languages, but learners aren't taught this because, well, it might make their heads explode. And since the Gaelic languages are increasingly dependent on second language speakers for their survival (and in Manx's case, completely so), they are losing this level of nuance. It's not Anglicization so much as just an inevitable loss when a living language is no longer the majority of speakers' maternal language.
I tried not long ago to try to explain this on Duolingo but I don't know if it made a lot of sense to people there. Learners often just want clear-cut rules about what's right and wrong, because often that's what they need at their level.
Michael Bauer, aka akerbeltz, whose main linguistic focus has been Gaelic, has the only write-up about this online or in print that I know of. He describes agus
as a "unspecified conceptual link
" that can morph in meaning and nuance. The examples he uses are more complex structures than [proposition] + [noun] + agus
+ [noun], but according to one of my former Gaelic teachers from Cape Breton (where some aspects of the Western dialects lost in Scotland have been preserved), this can happen pretty much anywhere agus
The way my teacher described it, the Gaelic languages--at least historically--presumed that the listener wasn't stupid and could derive meaning from context. We see that in a lot of languages, like in Russian or Japanese, although in those languages, it's often more about what isn't said, whereas with agus
, we have this Swiss Army knife of a word where it's up to the listener to infer which thingy-a-bob on the Swiss Army knife needs to be applied. And this can include dependent clauses and prepositional phrases. However, it seem that agus
was never meant to replace syntactical functions like declension, so the nouns still have to conform to whatever syntactical form they need to be in, like the genitive or accusative form, and that includes any applicable mutations or protheses.
As you can imagine, this would be a nightmare to try to teach learners. Moreover, it's sadly one of those aspects of the Gaelic languages that really stems from a deep, intuitive grasp of the language--what my teacher liked to refer to as "deep Gaelic"--something that is increasingly rarer in the contemporary speaker population. And in the case of agus
, aside from very old speakers, it may be completely lost, save for examples of it in older literature.
I have yet to come across documentation of this specifically for Irish, although I know from some older native Irish speakers I've talked to over the years that historically, agus
has been treated the same way in Irish as well. It just seems that in Irish, the pedantry, prescriptivism and reactionary knee-jerking that comes with teaching a standard form has really taken root, so it may be something further back in the memory of Irish than in Gaelic. Just keep in mind that on average, the speakers/learners online are typically younger, so what opinions and knowledge you are able to find online will generally reflect that.
(And this is why I often call Michael Bauer a treasure to us Gaelic learners, because if it weren't for his very Germanic sense of detail and documentation--yes, he's German-born--in his Gaelic linguistics research, I may have never known to even ask older speakers about this.)