How can I ask such a question? I don't want to write only for my question to be put on hold for being off topic, but I'm stuck with my main characters. Also, how does the sandbox work? How do I use that? Like a tag or do I need to do something more complex?
You probably shouldn't be asking about specific characters here on Worldbuilding.
https://writers.stackexchange.com/ may be a better fit. They have tags specific to the purpose:
Be sure to checkout their help center and be sure your questions are on topic before posting.
The sandbox and directions for using it can be found here:
For how the sandbox works, see the sandbox question post!
For characters, you don’t. See discussion here on meta on the policy of too story based.
I’m using the “Joe” test. If the question postulates a world and does not ask for any guidance in shaping that world, but asks instead “What would Joe do?” than it’s off topic.
Originally, we had a close reason for being individual or character based. This got folded into “story based”.