An LLC will protect you from most liabilities and is probably the easiest way to protect yourself in this case. Worst case scenario they sue the company and get all $0 worth of assets from it (assuming no sales).
Applying for an LLC is fairly simple and straight forward. Most states allow you to create one online for less than $100. It honestly takes less than an hour to set them up. Beware the tax implications of doing so, it's a pass-through entity meaning profits and losses are passed directly to your personal income. This is usually not a big deal and most tax software makes this very simple to document at tax time, just keep a record of all profits and expenses.
This is just from experience so take it with a grain of salt. Hopefully this gets you started with some further research.