When you syphoned off to new DJ's you will have taken up enough live yeast to get the ferment going again, well it is difficult not to get some live yeast.
Was the original still bubbling when you syphoned?
If it had stopped before transfer then the transferred lot will also not do any more.
2 weeks in a bucket is too long, I tend to put mine in for 5-8 days then into a DJ.
Could have used all the sugar - do you actually mean 4.5lbs per gallon?
If so that is a lot of sugar and would give a starting gravity of about 1.150 to 1.160 and so potential alcohol of 20-22%. Few yeasts will go to this level, most taper off at around 18% also the sugar concentration could have been too much for the yeast and it has given up. The grape juice will also have had a sugar content.
So what could have happened is that after 2 weeks the yeast has eaten as much sugar as it can, produced the maximum alcohol level that it can then died. Could also have run out of nutrient.
Does it taste sweet ?
If you put 4.5lbs in 2 gallons then the yeast will have eaten all the available sugar and wants more. It would now taste very dry. If you have done this then add 1 teaspoon of sugar to one of the DJ's, stick the air lock back on and see if bubbles appear. If this is what you have done and it starts bubbling a little then you will need to add about 1/2lb of sugar to each (a total guess but that would make about 2.75lbs a gallon) and the yeast should restart as it will have available food. Add a bit more nutrient if it starts going again.
Finally, and no idea what to do, rhubarb is acidic and the acid could have killed the yeast. No idea if there is a solution to this at this stage of the fermentation.
That is my offerings.
Rather hope it is dry as a bone to taste as this is likely the easier to sort.
If you can then drop a hydrometer in and find out what the gravity is.