How to make a process wait for the 'brothers'

The problem is that you are putting the wait() commands before the fork() commands that create the next processes. For example, on P2, before running the wait() you expect P4 you should run the fork() that creates P5. Similarly, in P1, before running the wait() you expect P2 you should execute the fork() that creates P3.

The code would look something like this:

#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <sys/wait.h>
#include <time.h>

int main(){
    clock_t t;
    double time_taken;
    t = clock();
    int status;
    pid_t idProcesso; // P1
    pid_t idChild; // Aby child process
    printf("I'm P1: %d  |  my dad: %d\n", getpid(), getppid());
    idProcesso = fork();    

    switch(idProcesso){
        case -1: exit(-1); //ERROR
        case 0: //P2
            printf("I'm P2: %d  |  my dad P1: %d\n", getpid(), getppid());          
            idProcesso = fork();
            switch(idProcesso){
                case -1: exit(-1); //Error
                case 0: //P4
                    printf("I'm P4: %d  |  my dad P2: %d\n", getpid(), getppid());
                    sleep(5);
                    break;

                default: //Continue P2
                idProcesso = fork(); //P5
                switch(idProcesso){
                    case -1: exit(-1); //ERROR
                    case 0: //P5
                        printf("I'm P5: %d  |  my dad P2: %d\n", getpid(), getppid());
                        sleep(5);
                        break;
                    default: //Continue P5
                        idChild = wait(&status);
                        printf("I'm P2: %d  |  Already waited for my son: %d\n", getpid(), idChild);
                        idChild = wait(&status); //P2 waits his son P5
                        printf("I'm P2: %d  |  Already waited for my son: %d\n", getpid(), idChild);
                        break;

                }
            }
        break;
        default: //Continue P1
            idProcesso = fork(); //P1 creates son
            switch(idProcesso){
                case -1: exit(-1); //ERROR
                case 0://P3
                    printf("I'm P3: %d  |  my dad P1: %d\n", getpid(), getppid());
                    idProcesso = fork(); //P3 creates son P6
                    switch(idProcesso){
                        case -1: exit(-1); //ERROR
                        case 0: //P6 son of P3
                            printf("I'm P6: %d  |  my dad P3: %d\n", getpid(), getppid());
                            sleep(5);
                            break;
                        default: //Continue P3
                            idProcesso = fork(); //P3 creates son P7
                            switch(idProcesso){
                                case -1: exit(-1);//ERROR
                                case 0: //P7 son of P3
                                    printf("I'm P7: %d  |  son of P3: %d\n", getpid(), getppid());
                                    sleep(5);
                                    break;
                                default: //P3 waits son P7
                                    idChild = wait(&status); //P3 waits his son P6
                                    printf("I'm P3: %d  | Already waited for my son: %d\n", getpid(), idChild);
                                    idChild = wait(&status);
                                    printf("I'm P3: %d  |  Already waited for my son: %d\n", getpid(), idChild);
                                    break;
                            }
                            break;
                    }
                    break;                  
                default: //Continue P1
                    idChild = wait(&status);
                    printf("I'm P1: %d  |  Already waited for my son: %d\n", getpid(), idChild);
                    idChild = wait(&status); // P1 waits his son P3
                    printf("I'm P1: %d  |  Already waited for my son: %d\n", getpid(), idChild);
                    printf("I'm P1 again, my id: %d\n", getpid());
                    t = clock() - t;
                    time_taken = ( (double)t ) / CLOCKS_PER_SEC;
                    printf("Time used in seconds: %f\n", time_taken);
            }
            break;
    } //SWITCH
} //Main

Note that this solution ensures that no process will wait for another to be created . However, it does not guarantee that the entire tree is created before processes terminate. If the process P4, for example, ends very fast, it may be that it has not given process time P7 been created yet.

To illustrate a more realistic case, in which the processes of the sheets perform a slower operation than a simple% of%, I have entered the break() at the end of each process. If you delete it, you may notice instances where some processes terminate before others have been created.