Good attempt. Especially since possession hasn't properly been covered yet. You have 2 mistakes here but only one which you have come across.
The mistake which you will have encountered is that the definite article (word for the) when dealing with plurals is "na". So na peathraichean instead of "am" (which would be singular).
The bit you won't have learnt yet is thar in Gaelic nouns which are owned go before the noun which owns them. So for example James has a car would be "tha CAR aig SEUMAS."
In this case, "the sisters have keys" would be "tha iuchraichean aig na peathraichean."
Yes. For some unknown reason, (a)ichean has become the most common plural for single-syllable words such as càr and, by extension, two-syllable words that lose a syllable during pluralization (such as piuth(a)r and iuch(a)r. It started in words that had a ch in them anyway but then spread.
Yes. We don't have cailín but the feminine caileag instead. But we do have boireannach for the new concept of 'woman', leaving bean for the original sense of '[married] woman' - tht is you only became a bean when you ceased to be a cailín.
I explain its origin here: https://forum.duolingo.com/comment/35373362?comment_id=37216339
We also have a word that is not animate, but is nevertheless a bit confused. Colin Mark gives it as
muir, mara (gen), marannan (pl.) (though usually given in dictionaries as nm in nom, nf in other cases, muir is very commonly fem in all cases) sea
The explanation given for this is that it was neuter and got a bit confused when the neuter was abolished. You will find the same word, which exists in lots of languages is of pretty random gender if you go to Google translate, put in the the sea (with the article so you can see the gender) and try translating into lots of languages used between Scotland and the Mediterranean.
Do you know why cailín is masculine as I don't?
Yes 'girl' is masculine in Irish. I have raided Wiktionary, following all the links and got no clue as to why. The Old Irish term caile 'maid' was either gender, for no obvious reason, and they stuck a masculine diminutive suffix -ín on it, suggesting that it was masculine on the day they stuck the suffix on. The Gaelic word caileag is essentially the same word, but with a feminine suffix -ag, suggesting it was feminine on the day that we in Scotland stuck a suffix on.
I am not sure on what grounds you think this should be accepted. I can see two possible arguments that you might have. One (which I don't think is very likely) is that you accept that got is the past tense of get which means 'obtain'. If this is the case then you are suggesting that this sentence means 'I obtained keys'. Well it doesn't. That would be
Fhuair mi iuchraichean.
The second (which seems more likely) is that you are suggesting that got can be used instead of have. I am not familiar with this myself, but Wiktionary gives it as
- They got a new car.
- He got a lot of nerve.
I have stated several times that we are limited by not knowing official policy on dialects, but there has to a limit to what is accepted. I think that we should, at the outside, expect that they accept
- standard US English
- standard UK English
- Lowland English
- Highland English
But there is a further problem when it comes to accepting non-standard forms. That is that the primary purpose of the English translation that you give is to show you know what the Gaelic means. When a sentence, such as I got keys, could easily be the result of misunderstanding the sentence, rather than a correct translation into a non-standard dialect, I think the only advice is to translate into one of the four types of English I list, to avoid ambiguity.
Of course this then leads to another problem, and that is that many people used dialect forms without realizing it. We often see this on this course where the given answer is in Highland or Lowland English, to th complete bafflement of Americans and even English people, because the course writers simply did not know it was not standard. They usually correct it when it is pointed out. And if this applies to you here, I am afraid you will just have to put this down as a learning experience. This is not considered standard English.