Can i marry my father's brother's wife's sister's daughter as per hindu marriage act

Father's brother's wife is to be called the paternal aunty (mother's co-daughter-in-law) and her sister's daughter will be called a sister.  Hence it is a prohibited relationship.

As per law it is prohibited relationship ,if you proceed  ,if you are ready to face consequence  it is yours(both) choice and how you face your family and society  is left to you.

already advised at https://www.lawyersclubindia.com/forum/can-i-marry-my-father-s-brother-s-wife-s-sister-s-daughter-please-reply-227522.asp

does not appear to be prohibited degree. Gorta of parental & maternal grandfather& grandmother should have nothing in common . As sister of the said girl is already married in the clan so there appears to be prima-facie no objection as apparently you are not sharing bloodline.