The plants will benefit from the larger pots, but that is not your problem. The soil you are using is not the greatest. I used MG soil before and had the exact thing happen. After a while the soils PH will start to correct itself with the addition of nitrogen, but until then you are going to have yellow plants. Give your plants half the dose of nutes it reads on the label every watering. Also, make sure your nutrients have micro-nutrients included. These are VERY important. If not a little CalMag might help.
If I were you I would try and get some promix. If you can't get any, make some soiless mix yourself. Get some perlite, vermiculite, dolomite lime and peatmoss. About 1 quater perlite, a half quarter vermiculite, the rest peatmoss. Don't forget to add three table spoons of dolomite lime (powderized) per gallon of mix. This might be possible for you to do if you can find the ingrediants. Usually any gardening store will have all you need. But the easiest is to just buy some promix.
Hope this helps and good luck!
TGT