If your parking lamps are lighting up (and I assume the license plate light and side markers are working as well) that would seem to indicate that you have sufficient ground capacity for the rear lighting harness.
Ignore the back-up lights for now. The problem is probably in the switch at the base of the steering column at the firewall - that can be dealt with later.
On the other hand, you
really need to fix your directionals and brake lights.
The directional and brake lights share a common filament in the double filament lamp. They are controlled by a fairly involved set of contacts within the MFS (multi-function switch) in the steering column. The hazard lights are also involved:
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Don't mean to bum you out but, quite often the problem you describe is caused by the MFS - and the only solution is to tear the column apart and replace the switch. It is a pain in the ass job.
But before you even think about that, do some simple stuff.
Open the taillight assemblies and check that there is a dual filament bulb in the correct socket - the socket with two contact buttons.
Make sure the lamp is properly indexed within the socket (i.e. so that the lower pin on the bulb base is in the slot that goes deep down and the higher pin is in the other slot).
Make sure that the socket is free of oxidation.
Some more bad news:
To go any further with this diagnosis you are going to need a multimeter. And, you will need to know how to use it - at least enough to check for voltage and continuity.
Do those things and come back.