Be careful. You should either be part of this company or get paid a set fee as a developer. Any other solution isn't stable. A company can't really survive w

Be careful. You should either be part of this company or get paid a set fee as a developer. Any other solution isn't stable. A company can't really survive with someone else owning its core IP (Option B), nor would they want to keep paying a perpetual cut for a product that you'll presumably complete/deliver at some point. If you want to go down Option C, take an equity stake.