I agree with the not easy comment.
The other 2 look well full so you could take some out of each and move a little over. It would not fill the 3rd but might help.
They look very clear to me, did you leave a lot of the bottom stuff in the previous DJ's? Thinking that you could prehaps have syphoned a bit more from previous, I usually allow a small amount of the sediment to get syphoned up at the first racking, also have the DJ's at an angle to get the most liquid out.
You say the SG is 0.990, that means that all the sugar has been converted, so I would not expect any further fermentation, and it will be dry.
This means that any sugar added will restart fermentation if you have yeast there to do it, this was why I asked if you left a fair bit at the bottom of the previous DJ's as you will have left behind some of the yeast.
The one option I can think of is to add white grape juice and perhap some sugar. Whether you take some of of the other 2 and add grape juice to all 3 or just the low one I would not like to say.
Fear is that if it doesn't really work then losing the low DJ is not too bad, losing all 3 is not a good idea.
What I would do:
If all are at 0.990 AND you do not want it that dry AND there is live yeast present, then decant some from the 2 full ones to a jug - say half a litre or more from each, add sugar (no idea how much, total guess 8oz) and dissolve it, Then add this back to the 2 fuller ones but leave more space - about half way down the shoulder of the DJ, an inch below the start of the narrower neck - then add whatever remains to the 3rd DJ.
Assuming the 3rd DJ is still low, add white grape juice to this, it will not detract from the body and will fill it up and be fermented as normal to completion.
This way you are adding sugar to the full ones to get the sweetness up, and not adding grape juice to them in case it alters the taste (I would not expect it to change it a great deal if any).
A fair conccern is the presence or absence of live yeast at this stage, but 0.990 means all sugar has gone and it is dry.