can you clarify me the resource planning issue?

Which issue ?

For the planning and management purposes, I would like to allow the team leader to see what his/her guys are working on.

All depends on what you mean by "team leader". There is no notion of team leader, only project leader.

Once I use the rules of access to the forms, I can manage to see only persons involved in his project or all.

That's right, it is designed this way.

Is there a way how to control the team?

No, there is no access control based on team. Team is only used to ease affectation and for some reports.

Thanks for prompt reply, that answers mostly my question.

The point was, that I wanted team control besides the project control. In my case, I have the Head of Mechanical Design group, who wants to see only his team in resources.

I will force him to use the reports, to have the overview over his team 😉

Thanks!