As this topic was created, I decided to share my opinion as well.
Currently, for a bank robbery there is a need of 10 official squad members. However, recently I noticed that the squad members are respawning or leaving the game, some on purpose, others maybe not, respawning as some other class or group just to prevent bank robberies.
(I) No matter what the spawn is, an official squad member should count. Earlier today, there were 5 official squads and 6 non-spawned.
(II) If the official squad member count is 10 and someone leaves, that count stays for 5-10 minutes more. For an example a gang is regrouping while there are 10 official squad members. On their take-off, 1 or 2 leaves and that way they can't start a bank robbery. So you could make it so even after they leave, they'd count for some more time.