OPTION ONE
I'm seeing two people from District 13. In my mind, I think parts of District 13 are still in tact. In fact, I see the district underground in a vault of sorts. Perhaps they second guessed the strike and sent some people to live in this vault. With the district destroyed, who would think to really poke their noses around there. More important things are underway, like the Hunger Games.
It's been over 50 years since the attack on District 13. It's presumed to be dead. Only, a small band of District 13 people are alive. They've come out of hiding and have decided that it is time to show the Capitol just what they're made of. Two kids are sent to two different districts (we'll say 2 and 7) around the age of ten. They sneak into the district at night when no one was looking. They magically just started to work their way into the everyday lives of the people there. Someone probably noticed them and they would explain that they were lost kids, orphans. When questioned about their family and surnames, they shrug and say they don't remember. Essentially, they are faking amnesia.
But how, do you ask, they get into the games. There DNA isn't on file. Ah, but you see, it is. Someone from within the Capitol, someone who works in the DNA labs, has slipped into the system two new entrees for the Hunger Games. As predicted, this person hailed from District 13.
You see, the people of 13 are smart and cunning. They waited to make their moves as they were small and few in number. But they honed their skills and spent a lot of their time preparing for this day. With their tributes sent to live in different districts, they would eventually begin a rebellion that will cause the gamemarkers to second guess the security and strength of the dome.
Back to the kids from 13, the Capitol doesn't know that they are outsiders. According to DNA records (falsified records) they have always been a part of the district they now call home. When the 71st Hunger Games roll around, the two volunteer as tributes. They can be anywhere from the age of 16 to 18 and are fully capable of winning. Only, they aren't in it to win it. No, they are in it to break it.
These two 13ers could be related or they could just be friends. Either would work. Lovers? I would probably avoid that. Love isn't something they can afford if they want to break the Capitol from the inside out.
Regarding the ending on the 71st games, the Capitol would be forced to air a rewrite. They would use holograms to make the ending. They would also kill off everyone, ensuring that no one leaked the truth about what happened. What did happen? Two tributes vanished. They just up and vanished. They removed the trackers from their body and, under that invisibility, they escaped. But why escape? Well, because they needed to learn how the dome worked. They needed to understand the mechanics behind it, especially if they were going to bring the whole thing crashing down.
There goal, the only goal they have, is to expose the Capitol and show the world just how weak they really are. They might have guns and power, but they haven't the resolve to survive nor the heart to make a change. District 13, having lost everything, has nothing to lose. They'll be the ones to start the fight, and the rest of the districts will be the ones to finish it.
So, no, there are more people from District 13. There's probably 16 of them. Two are pretending to be from other districts. One works in the Capitol. Two more work as guards for the Hunger Game drawings (again, to make sure the DNA reads correctly). Three more are working on footage to show the flaws of the Capitol. Five more are working on setting up communications between the other districts to spread the word of rebellion. And the final three are an elder with a wealth of knowledge, a nurse who knows a lot about herbal medicine, and a hunter who trained the tributes since the day they were born.
Will we play all these people? Probably not. The main characters are the two tributes from 13 that are disguised as tributes from 2 and 7. Other tributes from the HGames will also be playable, as these two will need more allies. They'll have enemies, too. In the end, I would say no more than 3 escape and the rest were either killed during the duration of the Game or were offed by the Capitol after the dome-breach to prevent any rumors from spreading.
OPTION TWO
Just a good old-fashioned Hunger Game inspired story. But let's make it so everyone but one doesn't die. Perhaps we use the HG theme, but make it our own.