Benoytosh Bhattacharyya died in 1964.  So his copyright expires and his works become public domain in 2024, 60 years after his death (http://en.wikipedia.org/wiki/List_of_countries%27_copyright_length.  The (C) rules specifically within Indian borders are laid out here, and seem more relaxed than the various international legislations (to which India is also a signatory): http://copyright.gov.in/Documents/handbook.html.

But the consensus in copyright discussions is that critical editions are different from monographs or literary works, and the consensus is that their copyright only extends to 25 years after publication.   This is law in Germany (but may be reviewed soon), and is emerging as general usage elsewhere.  So if the Sadhanamala vols are just edition,  or we're talking about scans of just the edition parts, then they've been in the public domain since 1985. 
See

• Margoni, Thomas and Perry, Mark, "Scientific and Critical Editions of Public Domain Works: An Example of European Copyright Law (Dis)Harmonization" (November 18, 2011). Canadian Intellectual Property Review, Vol. 27, p. 157. Available at SSRN: http://ssrn.com/abstract=1961535

Best,
Dominik