Launch your qsub jobs, using the -N option to give them arbitrary names (job1, job2, etc):
qsub -N job1 -cwd ./job1_script
qsub -N job2 -cwd ./job2_script
qsub -N job3 -cwd ./job3_script
Launch your script and tell it to wait until the jobs named job1, job2 and job3 are finished before it starts:
qsub -hold_jid job1,job2,job3 -cwd ./results_script