The ISS has an orbital velocity of ~28000 km/h; the velocity $v$ relative to the landing site of the descent module is probably even higher than that most of the time. Once the occupants have landed, their velocity relative to the landing site is zero.
My first question is: what is it that eliminates the velocity between detaching from the ISS and arrival? Three things come to mind:
- the spacecraft (Soyuz) engine,
a. descent module only,
b. descent module with parachutes deployed,
- the earth itself (final impact).
My second question is: how much does each of these modes contribute (measured in $\Delta v/v$ or $(\Delta v/v)^2$)? For the sake of the occupants' prolonged joy in space travel, I figure 3. has the smallest impact (pun intended), but how do the others relate to each other?