My doctor and the pharmacist said it was ok to take 300 wellbutrin and 60 cymbalta (duloxetine) just to watch for symptoms of it being to much can it cause seizure?

Yes, it can happen. That is the increased risk of taking those drugs in combination. Do you find them effective? Have you tried talk therapy? Do you suffer other side effects? Some people are more or less comfortable with psychotropic meds at any level. Trust yourself and talk with other doctors if you are not comfortable. It is a personal responsibility and it is part of your recovery.
Seizure. It is possible to have seizures on this combination. But it is very very rare. I used it but never seen a case in the last 10 years.