Your plants, from what I can see, are fine. Even the "dying" ones, though only time will tell, of course. Yellowing leaves happen; when they contain no more chloryphyl (i.e., they turn completely yellow), just pull them off. I have no idea why, but the plants are drawing extra energy from those leaves. Snip off any brown spots on the edges, and don't worry about hurting the plants. You could cut off almost all of the leaves without it being a problem. As an earlier poster said, cannabis is a very forgiving plant. But I agree; 90 degrees is too warm- you want to keep the temperature in the 70 - 80 degrees range, closer to 70 during the early vegetative stages. It's best to keep it hovering around 75, if possible.
Also, I know you don't care about yield, but I know of a way you could nearly triple your yield using the exact SAME amount of space as you're using now. It's called the ScReen Of Green method (or SCROG), and it's a variation on the Sea of Green method. It's simple, and requires virtually no effort. And since whatever strain you have seems to stay low and branches pretty profusely, they're born for this kind of operation. Here's what you do.
Buy some cheap chicken wire from the store (or use strings tied together if you must, but that takes longer to set up). You want the chicken wire to have holes at least 1" in diameter, 2" if possible (most varieties are two inches). Simply cut the wire to the shape of your computer, and duct tape it in a little bit below where you would want your plants to flower. Train the branches along the wire using twist ties (like the kind the come off of bread and bun packages), and train them all along the screen, using as much space as you can. With an overhead light, you'll have to trim stuff that pokes through the top. If you can, position your light on the sides so the sprouts off of the main branches don't try to make a break for the top of your computer. It's fine if you keep it where it is, though. If you know how to trim correctly, you'll even get more of it. Or you can just train the sprouting branches along the wire too.
Fill up the wire with your trained plants. And then allow the pre-flowering tops to poke through when you want to flower, and switch the light to 12/12. Voila. You've used the same amount of space with just a tiny bit more effort, and you'll get the kind of yield you would off of a 4-6 foot tall plant, maybe even a bit more. This method was designed for people doing stealth grows, so they could get the most out of it.
So, I'm sure you wouldn't mind having a little bit more than an 1/8, and instead having a few ounces. It takes virtually no effort, seriously. You just have to watch the plants (to train them), which I'm sure you're already doing since this is your first grow.
Oh, and in the vegetative stage, keep the light close to plants for the most profuse growth (as long as it doesn't turn the heat up on the plants too much). 2-4 inches is preferable, and adjust the light accordingly as they grow. Your plants will thank you for it.
Good luck!
~Will
