Translation:I am home, big sister.
I never feel quite right specifying "older sister" or "big sis" or whatnot in the English translation. I know it's necessary to cover the meaning of the Japanese sentence but it never stops feeling stilted and weird in English.
I heard "big brother" said in Fire Emblem enough that it now feels somewhat normal.
The usage of おねいさん is a bit out of context for me. If I say "I'm home" that usually means I'm in my own home. Why would I address my own sister with this polite form? Can ただいま、あね be used if I'm addressing my own sister?
So from what I understand, even with your own family, if someone is older than you, you use the same title to address them as the one you use when you're talking about other people's family members. They're older than you, so you show them respect. So "お母さん、お父さん、お姉さん、お兄さん". Of course in real life that often gets shortened to "kaasan", "tousan", etc etc, but that's a really informal colloquial sort of thing, and so isn't going to appear in Duolingo.
If you're addressing your own family members who are younger than you, you generally address them by name.
はは、ちち、あね、あに are not informal forms but rather sort of like... humble forms. You use them to refer to your own family when talking about them to other people
How would it work in larger families where you have let's say 3 older sisters. Would you then say "お姉さん" to address a specific one or is there a simpler way?
I think it is because she is older than you, so you have to be more respectful.
I think you have to use "big sis" to make sure Duo knows you know this is specifically for addressing the elder sister.
Duo does accept "I'm home, sister." though. That's what I got corrected with when I wrote the sentence above.
ただ means "just" and いま is "now", so a literal translation would be "Just now!" which is obviously not a complete sentence. This is a set phrase and, like many set phrases, it is an abbreviated version of a longer, unspoken sentiment. In this case, it means something like "(I've came home) just now." or "Just now (I returned safely)". It gets translated as "I'm back" or "I'm home" quite frequently, because that matches how it is used pretty well.
Is it wrong to say "nee-san"? I've seen it more commonly that "onee-san" in animes.
"Onee-san" is more polite than "nee-san" I'd guess it varies among siblings or something
"O" is an honorific prefix for substantives. It isn't that necessary, but is more polite, remember that in Japan the politeness is very very important.
The お particle apparently makes it formal, just like in the examples about bathtubs where there's an お before ふろ
I have that same profile picture on a different site; got really weirded out when I saw someone had the same idea o__O
My answer: "I'm home, sis"
I mean I feel like this sentence isn't that formal (considering you're home) so contractions should be fine?
It may have been the "sis" part that was the problem. For practice's sake they likely want you to specify "big sister" since there are different terms for younger and older siblings