How do I file my tax and get a refund if I work 1099?

Hi, I was advised by my tax lady that all I had to do is pay an estimated tax of 10% on what I make every quarter, which I have been doing. My question is how do I file my return and get a refund and do I get any money for my kids? I always file with W-2 so this is the first time I am only filing with 1099. Any idea will be very much appreciated.

If you work in New York and live in NJ, how do NJ state taxes work?

I know if you work in NY and live in NJ, you still need to file taxes. However, can you actually be double-taxed? For example, can one actually OWE taxes in a state they do NOT work in? I’m only asking because my gf’s accountant is telling her she owes a lot of income tax for NJ state, even though she doesn’t even WORK in NJ. I’m questioning this. Any feedback is appreciated.