don't worry about leaves falling off...you shouldn't have any bottom leaves fall off if you are keeping her healthy in veg. If you haven't watered in awhile then yes...water them. I would look for a small bottle of that root stimulator to soil feed the sick ones. And they aren't necessarily sick..I am not sure what all nutes are in the soil but you said you aren't feeding them anything but water and it looks like either you ended up getting some early stage nute burn or light burn a bit...I cant tell from the pictures but here is some good news...its been 3 days and they are all still green!!!!!!!! So that means they will survive as long as you keep a good eye on them. Also, like i said earlier, you should put them in their final pots whenever you want, but I would do it once they look a bit healthier or once the second leaves come in and look healthy. If you put one of them in the final pot and not the other two...there is a chance that that one will grow faster than the other two and you will end up with stunted plants. ORRRRR you could transplant all of them now and that would give them all more root development and even might help the sick ones out growing new roots and becoming more "established." Hmmm....now that I think about it I would do it now with all of them even with their slightly sickish look. But be careful when you do it and don't damage any roots and make sure you have clean washed sanitized hands before you handle them. Best way to handle transplanting in IMO is to wash your hands and then get them real dirty with the soil then you minimize the chance of infection on the gentle roots. Pick up the root stimulator mix and use it same day you transfer them. That will help also. Here is what I recommend you get also when you get some dow.
-2 T8 Soft white flourescent lights that are 4ft long or get 4 2 ft long ones. I say get T8 because T5 is more expensive but check out the lumens and how much K they put out. Each plant should have 7,000 lumen output for a normal grow speed. Anything less will make them grow slower. I have an auto under 3000 lumens right now and she is slow growing and it kind of forces her to not flower fast but to get short and bushy before she does. You want light spectrum of 6500 which is a cool blue / soft white light mixture. This is best for veg stage plants. Here is a good reference to read on the T8 ->
http://www.lrc.rpi.edu/programs/NLPIP/lightingAnswers/t8/02-t8-light-output.asp
Walmart should have some cheap T8 lights (or home depot) that put out about 3200 lumens per bulb. Don't try to get extremely lower wattage because the lumen output will be crappy also..and to be honest you wont be using much energy with a 24/32 watt CFL. I got 18 watt T5 bulbs by accident and spent like 27$ for each of them. I didn't research enough on it when I was reading about T5 bulbs but I have managed to grow 3 NICE size plants under these two 2ft T5 lights. I also had to cut cords and ghetto rig them up because they didn't have plugins lol. I bought the lights at home depot haha and got home and was like "where the hell is the plugin" So I took some exension cords with grounds on them and self twisted the cords together to get it to work. I will post a picture of my babies in my veg closet just so you can see what I is possible to do JUST with low output T5 bulbs.
So to recap, Get 4 short 2ft ones if you have a small space to work with and that will be 3200 lumens each X 4 = 12800 lumens. That will be sufficient for 2 plants. Or even 3 but will slow the growth if you add a third plant because it is not 21000 lumens. Like I said for a good normal fast grow each plant should have 7000 lumens with a color output of 6500K (blue spectrum dominant). Just know that your plants are probably growing slower right now because they aren't getting the blue spectrum they need. They are under red HPS bulbs (which is best for flower).
1. Get the root stim
2. Transplant all plants into the 3 gals individually
3. Water with root stim mix then foilage spray bottle the leaves right after you transfer them.
4. Mow some lawns if its not winter where you are or do something for your parents or guardians or someone you know to make a quick 60 bucks to buy some veg lights and get them under those lights until flower.
5. Watch this motivating video about hydro grow
--> HERE:
http://www.420magazine.com/forums/420-grow-videos/75953-how-grow-green-mr-green-pts-1-9-a.html
6. Relax and just know they will pull out of their slow growing stage and sickness. I got 2 random plants under my HPS light a week or two ago and I will show you what the HPS is doing to them since they are getting more red than blue spectrum. You will see what happens to them and the difference (the sick look and stretching). Will post pics in about 10 minutes for ya.
Again, dont worry this is your first grow and we all end up making small mistakes but its a learning process and you cant be perfect the first time nobody is and if they say they were then they are liars and trying to 1up you for some idiotic reason or compensating for other reasons lol. BB with pics bro.