Krista,
You'll be best served hiring an attorney, NOW! The fact that you asked such a question in an open forum like this demonstrates pre-meditation. Having worked in law enforcement for a number of years, I can certainly promise you, if anyone in that group you describe is injured, threatened, or even looks like they were attacked, YOU have just become the prime suspect!
Also, the atorney you hire can advise you on the differences in both civil and criminal liability by maintaining a firearm on your business premises as opposed to your personal residence. The rules are very different.
If someone trespasses, your best option is to call the police. If they offer threats or damage to property, or harm to people, they become liable. Talk to your attorney!
Good Luck!
Source: http://www.abusinessmentor.com