squash

This is a call to the old pros; HELP!

I spent every dime I have to grow 3/3 plants according to Colo. law (medical MJ patient). They got 3-4' hi, started flowering and some gnats got into them. I was told the gnats lay eggs and the eggs hatch and the grubs eat your roots. 3 of the plants developed brown leaves and stopped growing, turning light green....help!

I was told:
1) spray with garlic tincture. I did this on all the leaves top and bottom. stunk to hell. Sprayed the walls of the grow closet also; gnats and lady bugs all split town.

2) put tobacco on the dirt and water them to get 'backy juice on the roots.

3) Take plants out of pots, wash roots with soap, repot in new soil.
OK I'm broke but if I could do this won;t the plants die? What soap can I use and not kill the plants?
Also if I do this can I put the dirt in a big pan and bake it in the oven to kill the grubs etc> Will the dirt be oK then?

Thanks, I am a poor old man I cannot afford another tragedy; tell me they can be saved !!

Peace,
Squash, AKA Matt