You need to seek the services of a good Genetic counseling department. This is based on the little knowledge that I have.
1.It is common in South Indian for such marriages within families. In medical terms, this is termed as Consanguinous marriages.
2.In your case O positive and O positive should not be a problem. Generally, if the mother is blood group(A,B, AB,O) negative, father is (A,B,AB, O) postive and the first child is (A, B, AB, O)positive, then the second child can have some adverse effects.
3.In simple terms, we inherit our genetic imprint half from each parent. In cases of marriages within blood relative sort of dilutes the gene quality if there have been multiple consanguineous marriages among the families of your father and mother.
4.In Consangionous Marriages, unions among cousins like this are better than a marriage of Uncle and Niece, a girl marrying her mother's younger brother.
5. What you need is with the help of your parents looks for hospitals offering Genetic Pre-martial counseling.
6.Here a detailed family tree history with the specific focus of marriages among blood relatives, the presence of children with underdeveloped mental status, abortions, early age diabetes, hypertension or some types of anemia, children with a congenital disease will be assessed. These professionals will give you a medical opinion about the presence of any risks, if yes, the chances of those risks.
You don't need to worry too much, please seek the advice of Pre-martial Genetic Counsellors who can be found in large teaching medical college hospitals, corporate mother and child units.