I believe this may be "Road to Recovery" by cywsaphyre. It has Harry Potter recovered from Azkaban at the beginning of the fic, catatonic. Sirius is alive. The twins did indeed try to break Harry out of Azkaban, and later take him to their shop. And Harry does connect with the Prewetts and their children, in particular Lily, the youngest.
Here's the summary from the page:
Since turning fifteen, Harry has spent seven years in Azkaban. Now that his innocence has finally been proven and he is released, what will it take to get the former Harry back? Will they ever be able to? And what happens with Voldemort now? AU.
The relevant bit from where the twins describe trying to break him out.
They fell silent when Harry finally put aside the empty bowl, observing him anxiously. Harry looked back at them, resting an arm on a raised knee.
"You really tried... to break me out?" Harry asked at last.
George exchanged a glance with his twin. "Well yeah," He nodded, leaning forward a little. "You weren't supposed to be in there."
Fred looked rueful as he flopped onto his back. "Didn't work though, and we couldn't try again. We weighed our chances of course, but the probability of getting caught was too high."
The scene where he meets the Prewetts:
"Definitely," Harry hesitated for a second before smiling a little awkwardly. "And... we're kind of friends already, aren't we?"
Lily beamed at him, and Harry wondered at the ease in which children accepted things. "Yeah, we are!"
"Exactly, and you haven't even left the station yet," Harry grinned again when Lily's light brown eyes brightened. Harry could swear he had seen them before.
He rose to his full height again, only to blink and turn when Lily's gaze strayed behind him and she started waving excitedly. "Dad! And Uncle Gideon too!"
Harry was very, very careful not to let his jaw drop. A detached part of his mind realized instantly why the little girl was so familiar to him as he looked up to meet two pairs of brown eyes.
He had never even seen a picture of Fabian and Gideon Prewett, but they could be no one else because their smiles reminded him of Molly Weasley and the mischievous gleam in their eyes reminded him of the twins.
And indeed, they had issues with memory loss, and one of them got married.
Fabian's jaw tightened. "I had amnesia, Fred. I couldn't remember anything but my first name and Gideon. The Muggle police helped me get set up with a flat and some money, and then I found a job and waited for Gideon to wake up. I lived under the surname Purcell. Knew it had something to do with a 'P'."
"And I did," Gideon took up the story. "Wake up, that is. Obviously. Thing was, I remembered everything. But by the time I came out of my coma, three and a half years had passed. The war was long over, and I had an amnesic brother on my hands." He paused, and then amended, "An amnesic brother with a Muggle fiancé. If we had simply shown up on Molly's doorstep like that, we would have scared her out of her wits. And Fabian not remembering anything about her would be like him dying all over again. It would've crushed her. So I thought we could wait. Just until Fabian got his memories back."
"I remembered everything two and a half years later," Fabian recalled gravely. "But by then, I was married and I had a kid. It was lucky Heather, my wife, accepted it easily enough, or I'd have been looking at a divorce." His smile turned fond. "She was quite fascinated by magic. Asked tons of questions about it, and when Aster, my oldest, started showing signs of accidental magic, she was ecstatic."
There is a Death Eater attack at Kings Cross Station, but it's the narration that labels Harry's actions 'brave or stupid':
"We can't just leave!" Harry said aloud, not looking away when the Death Eater holding onto the girl raised his wand in a taunting manner as a man who must have been her father threw himself forward, obviously begging for mercy. "The Aurors aren't going to get here in time!"
"Harry, I know how you feel but there's too many people," Fabian looked frustrated as even Heather had stopped urging everyone away to watch their exchange. "We start a fight and people are going to get killed."
Harry's eyes darted around the platform, taking in the many people jostling each other to get to the Apparition point first. A sudden calm fell over him as an idea came to him, strangely comforting in its sense of familiarity of impulsiveness.
Some would say it was brave; others would say it was plain stupid. But Harry's best plans had always been spur-of-the-moment ones, and with unexpected clarity, he knew it would work this time.
I found this on the second page of Google search results for harry potter fanfic azkaban prewett twins.