Welcome to YT - What a wonderful thing you did.
YES - it is going to be difficult and sad at times, BUT you CAN make this work...baby steps...Get some books on how to deal with Shy and Scared dogs. Go slow, try to work on potty training, positive praises and a really yummy 'potty' treat should help the training along. You will need to try and build their confidences, there are books to help you with that too, but teaching them simple commands, believe it or not, will help build their confidence. Now, I will not lie to you, you may be in for a longer road with them, but in time you will start to see the improvements and changes and soon you will see happiness and love in their eyes, then you'll know it was 100% worth it.
Now for food, unfortunately Pedigree is not a very high quality food. I agree with you that they may need to eat wet food, or wet kibbles or smashed kibble inside wet food.
Here are some high quality brands:
Merrick (they have really appealing flavors)
Solid Gold
Canidae
Wellness
Nature's Variety
Innova
Please keep us posted - Again THANK YOU for saving these precious babies