Hello Natasha,

Yes, you should  renew it my dear.  Actually you should be renewing it for evry 4 years to be in safer side in the need of emergency. Since it is asked in majority during councelling for the exams .You should be renewing it. You need have the doccumemts such as,

Aadhaar card

Old caste certificate

10th marklist

This are enough for your renewal purpose. In case you are going to apply as a fresher you need have the caste certificate who are having the same surname of your family members. As you said it is okay to have your sister caste caertificate with same surname of yours. Please make a note of difference for applying for a fresher and renewing it.

Hope this is helpful.

Thank you.