which correct? in my fathers car/by fathers car
Please be careful to use correct capitalisation and punctuation in your posts. I have corrected yours above in red. Your profile shows that you are an English teacher. If that is correct, then you already know the rules of written English and it is very important to use them on the forum.
We would say "in my father's car" (if the context required it). Try to give us a complete sentence in future.
Remember - if you don't use correct capitalisation, punctuation and spacing, anything you write will be incorrect.