First, congratulations! This sounds like an exciting opportunity. However, part ownership/partnership can be tricky. What happens if you disagree down the road? What happens if someone gets sick, dies, or has to leave the company for any reason? What happens if there is a divorce and a spouse who isn't currently involved in the business also becomes a part owner?
Have you considered structuring your compensation to be salary plus a share of the profits without true ownership? That could potentially reduce headaches and liability for both of you.