First off, how powerful are the characters?
If they are starting out, neonates, they need to run. They aren't powerful enough, even working together, to hold on to much. All they have is a reason to be running away together.
It does allow a bunch of kids from different clans to clean together in a world were everyone is suspicious of them and wants to know "what they are hiding?" Beyond that, story ideas begin to get a bit sketchy.
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If they are ancilla (?) with some power, position, and contacts (who just happened to be out of the city that night ~ their elders sent them out on a mission ~ and on hearing the news of the 'terror' attack, they have elected to return home, because they CAN hold onto power.
They have enough power (and the roots) to stick it out against most other newcomers. They have an incentive together to hold on to what they have, knowing they are more powerful united.
Still, newcomers have to be somewhat welcomed because the Sabbat will coming looking across the border eventually.
Its a 'Who is Really the Enemy?' scenario.
Who do they allow to stay in the city?
Who do they make prince? How do they handle suddenly being the Elder with all the rights and responsibilities of said position (like the right to make Childer)?
How much is their clan going to support them? At what cost? And how much can those Machivellian Elders be trusted?
Thing grow from a Wild West feel (how appropriate), to a Boom Town feel (there is a lot of territory and status to carve up), to a 'Junior Elder's Club' feel as you have to deal with other established clans, Anarchs, the Sabbat, and even your own Childer.
And then you still have the mystery of who killed all those other vampires off. Good luck. Maybe they can find out what did it right as a Sabbat invasion is about to happen

. Now what do they do?
FYI, as an ST, I use a One Vampire per 50,000 person Rule. It is about double of what WW says, but I feel it gives a more accurate count for Caitiff and Anarchs, as well as the unnatural desire for Vamps to procreate.