According to the Tatkal rules of railway, only four people can travel on one Tatkal ticket. However, you can book two Tatkal tickets online at a user id. However, this arrangement is not available for the first AC and executive class. This is the rule of waiting ticket: If some seats have been confirmed on any urgent ticket, but some are in the waiting or RAC, then in such a situation, those with waiting and RAC will also be able to travel by train.
If you want to cancel the ticket immediately, then you can do this before 30 minutes of the departure of the train. But also keep in mind that if your Tatkal ticket is in waiting or RAC, then it will automatically get cancelled. If the seats of some passengers have been confirmed on any Tatkal ticket, but some are in the waiting or RAC, then those passengers who have waiting and RAC tickets will also be able to travel by train.