Query about relative definition u/s 56(2) of it act 1961

" If  A is relative of B as per sec 56(2) of it act, Inevitably then B is relative of A ?, Or We have to check relative definition again?

Yes, relation as defined u/s. 56(2) are exact and not reversible.

Gift to your BUA (Father's sister) is taxable, you are not her relative !!! Though for you she is....... (Of course, only as per sec. 56(2) of IT act)

Well, if it is [monetary] gift......... you can gift your BUA via your father.......

As gift to your father and additionally gift (of your father to his) sister are tax exempt !!