How many bystanders will help?
Jelly,  9 8  7 bytes
(Saved 1 when the assumption of sorted input was allowed, and another realising there was no need to floor the inverses.)
İ&lt;Jṣ1ṪL

A monadic Link accepting a list of floating-point numbers in \$[0,1]\$ sorted in descending order that yields an integer.
Try it online! Or see the test-suite.
How?
Effectively this evaluates how many people need to be in the crowd to stop each person helping, identifies crowd sizes that would be too big for anyone to help if those most likely to help have been removed, then counts those in excess of the biggest of those crowd sizes.
İ&lt;Jṣ1ṪL - Link: list of thresholds, T  e.g. [1, 0.34, .34, .25, 0]
İ       - inverse (T)                       [1, 2.94, 2.94. 4, inf]
  J     - range of length (T)               [1, 2, 3, 4, 5]
 &lt;      - less than?                        [0, 0, 1, 0, 0]
   ṣ1   - split at ones                     [[0, 0], [0, 0]]
     Ṫ  - tail                              [0, 0]
      L - length                            2


Equivalently:
İ&lt;JṚÄċ0
   Ṛ    - reverse                           [0, 0, 1, 0, 0]
    Ä   - cumulative sums                   [0, 0, 1, 1, 1]
     ċ0 - count zeros                       2