Wow! That is a lot of birds for such a small cage, thank you for taking them in and trying to make the best of this situation!!!
I'll address the questions not answered yet.
If they currently are not eating any veggies or fruit, then you may have a hard time convincing them to try out something new. However, don't give up !! If one bird decides to try it out, then the rest will soon follow.
The easiest foods to start out with are leafy greens. Spinach, Arugula, Parsley, Cilantro... Then you can try some broccoli, peppers, eggfood, ect.
Fruit is usually very high in sugar, and should only be fed once in a while.
If they are currently seed addicts, (which most birds are) you can start by improving their diet by sprouting the seeds you currently have. Here is a link to my sprouting guide. Keep in mind that there are many ways to sprout seed, this is just the way I do it, and I find it's the easiest for my routine. You can check out other ways in the nutrition forum.