In Vadakalai Yajur Veda tradition, during amavasyai tarppanam, how many darbha grass must be placed on hand and seat? In the thaambaalam (bigger-sized salver/tray), how many darbha grasses must be placed East to West in parallel?

For the seat, usually, two darbhas are placed, with one of them could even be a darbha with an uncut tip (nunippul). Some say as per “darbheshu darbhaam”, more than two darbhas must be used; some say 4 must be used.
For bhugnam, two darbhas are placed East to West in pairs. This is a seat for the Pitrus.