"Sizin" means "yours" but addressed to a group of people mixed or not! Exp: In the classroom, the teacher order his pupils to open their books, so he will say: (Open "yours books") So, yours boos her will be "sizin kitapların". While the other possessive pronoun "senin", means "yours" either, but this time the teacher will order one pupil to open his/her book: (senin kitabın ...) ! Nice day!
"Your apples" Translation: Sizin elmalarınız
"senin elmaları" must be accepted , right ? it was wrong, why?
Your English translation answer: The apples that are yours.
You used the accusative suffix "-ı." You are on the right grammar trail if you used the (genitive) case for plural apples as corrected below.
"Senin elmaların" - Correct.
Minditon, "elmamar"= "elma"+"lar" plural suffix= the apples. "elmalariniz" = "elma" + "lar" +"iniz", possession or ownership suffix 2nd person plural = "your apples". "Benim elmalar-im"="my apples", "senin elmalar-in" = "your apples", 2nd person singular, "onun elmalari (i pointless)" = "her/his/its apples, "bizim elmalarimiz (pointless i)" = "our apples", "sizin elmalariniz"= "your apples" and "onlari (pointless i) elmalari (pointless i). Have a look at this video, very clear: https://www.youtube.com/watch?v=bH2iRwfBFPs, or there: duolingo turkish grammar portal, both usefull. There are a lot of sites about this topic.
Front vowels: (e, i, ö & ü) a front vowel can only be followed by a front vowel. Example: "Silgiler" - erasers, in the example the root of the word is "sil" - to erase. We have added the suffix -gi to make the word "silgi" - eraser & the plural making suffix -ler to make the word "silgiler" - erasers. All of the vowels in the word silgiler are front vowels i & e. Front vowels (e, i, ö & ü)
Word examples: Birinci - first, köprü - bridge & çeşitlilik - diversity.
Back vowels: (a, ı, o & u) back vowels can only be followed by a back vowel. Example, uyanınca: uyan – wake up sleepy head, uyanın – wake up sleepy heads & uyanınca – awakened sleepy head/heads. All the vowels in the word uyanınca are back vowels. More examples: Kalkınca, soruyor, kırılsam, olmadın, olanları, kulum, kullarını & tanrım.
They can also be capital & lower case.