YES, in general meaning it is bigamy.
But if the concerned three has no objection, then according to ipc readwith crpc it does not attract the provisions of concerned bigamy law of ipc & crpc.
yes it violates the HMA, sec 5 & 5(i). it will be a void marriage u/s 11.
the concerned act runs thus
5. A marriage may be solemnized between any two Hindus, if the following conditions are fulfilled, namely:- (i) Neither party has a spouse living at the time of the marriage
11. Void marriages. Any marriage solemnized after the commencement of this Act shall be null and void and may, on a petition presented by either party thereto against the other party, be so declared by a decree of nullity if it contravenes any one of the conditions specified in clauses (i), (iv) and (v) of section 5.