They are correct, but they don't sound natural. I would say: These two pens are yours, and this book is mine. or These are your pens, and this is my book.

These are two pens and this is a book. The pens are yourS and the book is mine. These are some pens and this is A book. The pens are yourS and the book is mine. Plural PENS We normally use the word A to mean one book, in that sentence structure, and we pluralise the your to become YourS to match any plural at beginning of sentence.. If speaking one person to another this/this/it are your(S).... "This/it is your pen and this is my book".. ...If the second persons object is at front of sentence it is your X are you X(s) and my/mine Y(s) at the end of the sentence, use singular or plural to match either book(s) pen(s).

So, "yours" is the second person possessive pronoun, to go with "mine", or his, hers, (this one is very rarely used - its ), ours, theirs. You will see that there is no apostrophe - ' - in any of these words. When you use the possessive in front of a noun, as a determiner (like a, an, the, some) then the possessives are slightly different. My, your, his, her, its, our, their. https://dictionary.cambridge.org/grammar/british-grammar/pronouns/pronouns-possessive-my-mine-your-yours-etc https://www.brighthubeducation.com/english-homework-help/54178-possessive-determiners-pronouns-and-when-to-use-apostrophe/