Joining a startup, not sure how to proceed (worried)

TL;DR - Entreprenuer family member asked me to make application, lists himself as company. Promised me equity after I make "skeleton" of application. Signed NDA and IPA. No non-compete at current full time job.

Long version:

Throwaway because "coworkers".

I'm currently working full time at a software company as a mid-level developer. I enjoy my work, and they are very strict on having employees only work 40 hours a week. I tend to work on side-projects in my free time, and I currently have a lot of that.

I was approached by a family member with a history of fairly successful entrepreneurial ventures. Nothing crazy, but he likes to built up a company or product, then either sell his shares and leave, or stick around for awhile as a CEO. All mostly small and local.

He approached me with an idea (he has no tech experience) and asked if I would be interested in implementing it as a side-project. I found the project extremely interesting, so I offered to consult for free as a favor.

Soon after, he asked me if I would be interested in working on it directly, and rather than a favor, I would have equity in the company he would be starting around the application. Last week, I signed an IP agreement, and an NDA regarding the project.

I wasn't really thinking, but I realized as I was working on it today, that the "company" in the documents was listed as him since the company hasn't been formed. He is bringing in a close friend of ours and stated that once the company is formed he will distribute equity to us.

I am the sole developer of the project, and I have a few concerns.

• Can he drop me and steal my work at a moments notice?
• With three of us, what percentage should I be fighting for being the sole dev?
• I would trust him with my life, but does this seem sketchy? Or is this normal?

I'm worried I'll be throwing away hours of my time if something were to happen.

Is there any way to protect myself from anything happening? I've taken to recording what hours I work on the project, a timesheet I guess. But since I'm not an employee, I don't think that will help me much. I double checked with my work and I haven't signed a non-compete, they told me they have no concerns about it. So I'm good there.

Does anyone have any advice? I know absolutely nothing about startup culture, and the broader internet hasn't given me anything concrete besides opinions and horror stories. Is this sketchy? Or normal...

If I'm being oblivious to anything, please feel free to point it out. I'm afraid I've been viewing everything through rose-colored glasses.