Father's sister doughter marrige

If you are Hindu go thru 'prohibited Relations','Spinda Relations'.

It is your bua's daughter and hence your sister.

if u r hindu, u can not marry ur bua's sister becoz she is ur sister (first cousin)

Such marriage bring social stigma.

Such marriage have its own drawbacks and issues.

Central Government Act
Section 3(g) in The Hindu Marriage Act, 1955
(g) “degrees of prohibited relationship”— two persons are said to be within the “degrees of prohibited relationship”—

section 5 just lays down the requirements of a valid Hindu marriage but it does not lay down the effect if any of the conditions laid therein are not followed. This effect provided for in section 11 and 12 of the Act. Out of these two sections it is section 11 that deals with nullity of marriage.
 

Indian courts recognize custom as law only if the custom is “ancient or immemorial” in origin; “reasonable in nature and continuous in use”, and “certain”.




Courts interpret “ancient or immemorial" to mean that for a custom to be binding. it “must derive its force from the fact that by long usage it has obtained force of law”.

Ther are many threads on similar query at LCI and issues attached that you may find relevant and useful e.g:

https://www.lawyersclubindia.com/experts/know-about-property-act-602896.asp

Example AP CM Chandrababu Naidu's wife is Sister of Actor cum MLA Balakrishna, who is Hindupur MLA. Balakrishna's daughter  Brahmani was married to Chandrababu Naidu's son Lokesh.

HI in hindu marriage these realtion not allowed its probhited so  you could not allowed 

If your custom allows, it is valid otherwise it is prohibited.  What is customary sanction, has been unambiguously defined in Hindu Marriage Act.  In Andhra Pradesh and some other parts of Southern States, these marriages are not prohibited and they can be validly registered.  If you are not belonging to that areas and still want to go for this marriage, there is a way people in your predicament practice.  Both boy and girl convert into christianity and marry under christian law.  Before doing this, you consult the church and then only put a step forward.  In Delhi, one metropolitan magistrate got into same problem and he converted himself into christianity along with the girl and after conversion got married in a church.  His father, being an advocate, filed criminal complaint against the judge. the hon'ble High Court of Delhi (judge: Hon'ble Mr. Suresh Kait) imposed heavy punishment against the father and quashed criminal complaint against the boy and girl and validated their marriage.