What do I do about mu guppies?

I was really hoping a fish expert could answer but I really need to know. How to tell exactly when my guppy is ready to give birth, what a pregnant guppy looks like, and what exactly i need to do when she starts birthing if i don't have a breeding net/box. I really want my guppies to breed I have 1 mature male 1 large female who's gravid spot is really dark but isn't gaining much weight and one juvenile female who's gravid is also getting dark and she is getting FAT. The thing I noticed about their gravid spots is I can leave the light off for a few hours and their gravids turn completely pink! But after the light has been on for a while they become dark again! And finally ive noticed that they have silvery scales showing up on their flanks and around their mouths, and black and white patches on tails and fins i was wondering what this could be? I am new to guppies and have now clue what i'm doing :( I know this is a huge question but i really need help!