Sapinda marriages are not legal under Section 18(b) of the Act of 1955. The people who are performing such marriage and the people who are married may be punished by simple imprisonment for up to one month, a fine of up to one thousand rupees, or both.
Section 3(f)(i) of the above act talks about a sapinda relationship. It will be extended to the third generation in the line of descent through the mother and the fifth generation in the line of descent through the father concerning any person.
This relationship is always tracked upward, in the ascent direction. The computation of degrees takes into account both the individual and the common ancestor.
If these marriages are as per the customs of the people and are well accepted by the community, there will not be any problem. So it all depends on the practices in your family and community around. If nobody complains about this marriage, there will not be any problem.
In your case, your relation will come under Sapinda relation and not legal as per the act. But it all depends on your family practices. So it is always better to take the opinion of a well-known lawyer and then decided. I know many people whose relationship falls under Sapinda relation but are married and leading a happy life.