Yes, you could put it into the demijohns now that vigorous fermentation is completed. This will reduce the exposure to air. The thing to avoid is putting into a sealed bottle, as your wine will continue to produce CO2. Do you have an airlock for the demijohn?
If you don't, you could cover the hole in the demijohn with (and I am just making this up now) plastic wrap or something to keep unwanted stuff out, but not be an airtight seal. An airlock would be better, obviously.
If you don't, you could cover the hole in the demijohn with (and I am just making this up now) plastic wrap or something to keep unwanted stuff out, but not be an airtight seal. An airlock would be better, obviously.