I apologize for the length of the post. The last two paragraphs are a more brief summary. 

I began working with this company a year ago with the assignment of handling general office tasks. Very quickly I realized that there was many moving parts that very specific to the niche market that we are involved in, and I felt confident that I could develop an application for in house use to assist with daily operations and projections.

A year later, the owners (which I know very personally) and myself are considering moving forward with starting a separate SaaS business targeting the niche market that we operate in, building on top of the application I have already developed. The dilemma I have is rationalizing ownership within this theoretical SaaS company.

There are five owners in the current business I work for, and all 5 want to be owners and investors. Should I be satisfied with equal ownership between each partner, or should I have a larger stake?

At first I felt that I should have a heavier stake because I have put in effort to develop this software to its current state through late and long nights on the side of my current work, but the success of any SaaS product like this will be heavily reliant on their knowledge and experience in this market. The proposed structure would be biweekly meetings between sprints where they come in to provide their insight and opinion. I would also make the point that their connections within this market may prove useful down the road.

I could be satisfied with equal ownership between six individuals, with myself only putting in sweat equity, but I have the means to raise the funds to contribute, in which case my other option is to perhaps request 30% with the other 5 individuals splitting the remainder, and each member contributing the amount that matches their equity.

I am honored that they see enough potential in me to pull money out of their own pockets, and for that reason I am weary of coming across as ungrateful. So feel free to tell me if this all sounds petty or greedy. Thank you for any input you have.