Hi Nikita
It is possible to restrict access to course activities using a number of criteria including audiences .
There isn't a dynamic audience rule based on user role so you may need to add the trainers or facilitator manually or maybe use a custom profile field to indicate they are a trainer or learner.
if this isn't easily done then you could achieve this by changing the permission of the trainer and learner role for each seminar by going to seminar administration and permissions and delete the permission View seminar activities and events. This will only affect the selected seminar.
regards