"Club Soda" and Seltzer water are the same thing. Unflavored carbonated water.
Generally stuff you will find for sale has been artifically carbonated. Nothing wrong with this, just cheaper to do. They simulate naturally occuring "mineral water". This is Perrier. Water is forced up through mineral rocks where the water gets carbonated through a natural process. The same can be done by injecting CO2 into liquid. This is how Pepsi is also made.
They are one in the same. What you DONT want to buy is TONIC water or any flavored water. I always use Safeway Seltzer water. Cheap and unflavored.
You can mist at any time in the cycle if you know what you are doing. Mold is an issue in certain situations, so be alert. In the absence of any issues, misting is merely another way to get nutes into the plants. A leaf will absorb like a root. But you need to be careful: if you plants are nuted up (you will see the tips of leaves start to turn brown ie "burn" a bit) then forcing more nutes will only make it worse. Check your leaves. If they are 100% no burn or nute burn marks foiler feed. If you see burn dont force it. A root can withstand excess nutes far more than a leaf can. If you burn your plant, you will cry like a little baby girl.
In your pictures, I see they are green with slight tip burn. As noted above, (for a ameteur) I would not mist. You could burn them more. If you do, do a 1/4 to 1/2 recommended wait 4-6 hours and look. If they burn more, stop. But overall I think they look like they are getting enough nutes. Could be the strain. And the last plant may be bisexually confused. If they came from the same seeds, I would keep my eye on it. Not all plants turn out perfect.