"I am home, big sister."
In general, yes I agree, but おねえさん.and ねえさん are not the only possibilities here.
Also, people do use あね, and あねき and あねうえ, but I think Duo doesn't want to teach people to sound like yakuza. So, it's not that you can't use it, it's just not how it is generally used in Japan.
Well, I don't personally know any yakuza but they have an image in Japanese media/film/TV, in a similar vein to the image of a cowboy as portrayed in Western media, an exaggeration of an archaic version of the real thing.
Anyway, with that disclaimer out of the way, being an organized gang, a yakuza group has a rigid hierarchy between its members, which is usually based partly on age, with older members generally being more senior. As a way of showing respect, each yakuza member refers to any female members that are more senior than them as あね, あねき, or あねうえ.
I'm not sure what the difference is between the three: it might be regional, it might be historical, it could just be specific to each group. There may be other common honorifics, but these three are the ones that stand out to me as being stereotypically yakuza. More senior male members have the equivalents of あに,あにき, and あにうえ.
”ただいま”I am homeの発音がおかしいです。（笑） そして家族（かぞく）で”おねいさん”とは、呼びません。 弟young brotherなら"ねいちゃん"、"あねき"。妹young sisterなら"おねいちゃん"、 ”ただいま（只今）家に帰ってきました”I am home now." "おねいさん"義理（ぎり）の姉（sister in law） 只今just now,from now,at the moment, 只今他の電話に出ております。He is busy on another line. 只今会議中（ただいまかいぎちゅう）です。He is in a meeting now. 只今電話（ただいまでんわ）に出られません。I can't answer the phone right now.
It just depends what you're used to, though it is a bit of a hurdle for English speakers. In Hokkien, there are different words for "uncle" and "aunt" depending on whether they are on your mother or father's side, whether they are older or younger than your parent, and whether they are related to your parent by birth or by marriage, so this concept in Japanese was a piece of cake for me.
When referring to their own families amongst themselves, just like there's no "right" way for you to call your own father (be it "dad", "pa", "papa", "father", etc.), Japanese families would also each have their own way of doing things and there aren't really any rules. Depends on the parents, what names the kids picked up on as babies, the individual personalities, the specific family makeup, etc.