So cute!

I've only ever trained one puppy at a time and it took constant vigilance. I would even have the puppy sleep with me, so I could monitor him. They always have the walk off, sniff around when you know they're trying to find a place to go, so then I would rush them outside.
When they would go potty in the house, I would scold them, say "no, you go pee outside." and then rush them outside. If they went outside, I would give them lavish praise and petting and say something like, "you go pee outside, good girl or boy!" over and over.
If they whined, I'd immediately take them outside and tell them to go pee, etc. If they went to the door or scratched on the door, I'd do the same. A lot of vigilance and repetition and they'd be trained to either whine at me or go to the door and they'd know they got to go outside.
It took up all my time and it was with one puppy and they were trained usually in a week or 2 I believe. I don't know if this was the best or proper way, but that's how I did it.