You really should read the documentation to understand how things work.
PREEMPTION means that a task can be interupted at any point if a higher priority task becomes ready.
TIME_SLICING means that every tick interrupt, if another task of the same priority is ready, you will switch between them.
Since all you tasks have different priority, TIME_SLICING will have no effect.
Task 1 being the highest priority means that while it is ready to run, it WILL be running, and only when it finishes and blocks for its next time to run, will the next priority task run.
For a fixed priority real-time system like FreeRTOS, it is a contradiction of terms to say that a higher priority task gets held of at some point to run a lower priority task.