Details about Sapinda relationship

The third generation from your mother side when you go upwards and the fifth generation from your father side are called Sapinda relationship.
If the grandmother of you and your cousin is the same, your relationship will be treated as a Sapinda relationship.
Similarly, the grandfather of your grandfather and the grandfather of your cousin's grandfather are the same that relationship will be Sapinda relationship only.
If two persons come under Sapinda relationship, as per the Hindu marriage act such marriage is not acceptable here.
But in your case your grandfather from mother side is the brother of your cousin's grandfather from mother side. As such your relation can't be treated as Spinda relation.

The Hindu Marriage Act, 1955 has clearly mentioned the Sapinda relationship. As per Section 3 of The Hindu Marriage Act, 1955, it is understood that Sapinda relationship? with reference to any person extends as far as the third generation (inclusive of his present generation as first generation) in the line of ascent through the mother, and the fifth generation (inclusive of his present generation as first generation) in the line of ascent through the father, the line being traced upwards in each case from the person concerned.

It means that while upward tracing of line of ascent either through mother side or father side if they converge at the same person after 3 or 5 generations then such relationship is termed as Sapinda relationship. In your case they are diverging to different persons either at maternal side or paternal side so your case does not categorically come under this category.

One of the interesting thing from the legal angle in this matter is that if such a relationship is established then it will be legally accepted correct even if the relationship is by half (from different wives) or full (from same wife) or uterine (different husbands but same wife) blood. The law also does not differentiate between illegitimate blood relationship and legitimate one and also considers adoption as equal to blood relation.

These strange clauses were incorporated in the Hindu Marriage Act to safeguard against equitable distribution of the ancestral property as in earlier times the property remained same for generations till it was legally divided between the successors.