If there is no upset in stage 1 then the lowest seeded player who can win the tournament is -

In stage I, in a group in total 6 matches and that will have 12 points in total.
Total number of matches in this stage is 4 × 6 = 24
In stage II, total 8 players and they play each other except a player who comes from same group but point of their match in stage I is carried forward hence in stage II total points is 28 × 2 = 56.
Number of matches in stage II is 7 × ( 8/2 ) – 4 = 24
In stage 1 a player has to win minimum 1 match to advance to the next stage.
Now consider the different groups,
South Kolkata : 1, 8, 9, 16 [seed 9 can advance after beating seed 16 without an upset]
North Kolkata : 2, 7, 10, 15 [seed 10 can advance after beating seed 15 without an upset]
Central Kolkata : 3, 6, 11, 14 [seed 11 can advance after beating seed 14 without an upset]
Saltlake : 4, 5, 12,13 [seed 12 can advance after beating seed 113 without an upset] So seed 12 is the lowest seed who can advance to stage II without causing Upset in stage I, and can win the tournament [Please note here that in stage II or semifinal there may be an Upset