If Ekadashi falls on the sapindeekaranam (12th day) day, can the 12th-day rituals be postponed by one day or must they be performed on Ekadashi day itself using broken rice for preparations? If Ekadashi falls on a shraddha day or maasikam day, what must be done?

As sapindeekaranam is a saavakaasha kaaryam, it must not be done on an Ekadashi day and must be performed the next day. If shraddha and maasikam occur on an Ekadashi day, they must be performed on that same day. With regards to Sodakumbham, it is performed a day earlier due to Ekadashi.