Gender and Number

Neha knows "chai" (tea) is feminine — "thandi chai" (cold tea). She reasons that since "paani" (water) is also a drink, it must be feminine too, and writes "thandi paani". Is Neha right?

Rohan knows "kitaab" (book) is feminine — "nayi kitaab" (new book). He assumes every school item shares the same gender, and writes "nayi basta" for "basta" (bag) too. Is Rohan right?

Deepak thinks every word must change somehow to form a plural, so from "ek ghar" (one house) he makes "do gharein" (two houses). His sister says the word does not change at all here. Who is right?

Knowing that "ghar" stays "ghar" in plural, Meera thinks this rule applies to every masculine word, and writes "ek ladka, das ladka" (one boy, ten boy). Her brother says this is wrong for "ladka". Who is right?