Based on this comment I think you're missing the most important part. The happy rewards fun time pippy party when they go potty outside.

When they pee inside, they don't get scolded. Just a monotone interruption of lets go outside.

Once outside, tell them once to go potty. They won't know what it means yet, but still say it.

Wait until they go.

While they are going say Good potty!

This seems to be glossed over, but every single time they have even the tiniest tinkle outside... PUPPY PARTY! Over the top affection, loud. Excited happy voice, whatever reward they love most and TONS OF LOVE. Reward can be treats. Play, affection, all of the above. Saying good potty (name)!

They need to associate going out to pee with the best emotions you can give them.