Sentence Correction

Writing "yeh meri apni swayam ki kitaab hai" (this is my own self's book), Nikhil thinks adding both "apni" and "swayam" makes the sentence more emphatic. His sister says one word should be removed here. Who is right?

Writing "meri behen kal school gaya" (using the masculine verb form), Karan thinks the sentence is correct because every other word is in the right place. His mother says there is a mistake in it. Who is right?

Writing "mujhe vishwas hai KI vah aayega" (I believe that he will come), Tanvi uses the possessive "KII" instead, thinking "kii" and "ki" are just two spellings of the same word, either works. Her friend says the wrong word was used here. Who is right?

Writing "sabhi chhatragan upasthit the" (all the-student-group were present), Maanasi thinks adding "sabhi" (all) makes the sentence clearer, to show everyone was present. Her brother says this word is unnecessary here. Who is right?