I wish to begin the Ashtaka and Anvashtaka Tarpanam. A relative says this should only be done in the month of Masi. However, my friend and astrologer from Thanjavur, Shri G.K. Swaminathan, says it should be done during the Krishna Paksha Saptami, Ashtami, and Navami of four months: Margazhi, Thai, Masi, and Panguni. Please clarify this and explain how it should be performed. 

Those who perform the Shannavathi Shradha (96 ancestral rites) will perform the Ashtaka Anvashtaka Shradha in all 4 months. Others usually perform it in the month of Magha (Masi), specifically on the Krishna Paksha Ashtami falling between the Thai Amavasya and Masi Amavasya…they perform the Ashtaka on that day and the Anvashtaka the following day. This usually occurs in the month of Thai, and occasionally in the month of Masi.