Or you can sell it, split the equity, and go separate ways.I'm not a fan of borrowing from family/friends unless all parties are honest and everything is documented in a written contract.

I was lucky to split the sales over 2 years, so the first ~80k gain is tax free and 80-480k was at 15%, which I was able to take advantage of twice.

Normally, as @Jaycee Greene suggests, you make a management fee plus a split of cashflow with investors (oversimplified explanation).

Would I pay for all the remodel expenses and then 50/50 split of profits or does contractor pay remodel cost?

While a general contractor (GC) can help with this, it's good to have your own detailed plan to avoid misunderstandings.As for materials, you can either let your GC handle everything or split responsibilities—GC for rough materials (like lumber and drywall) and you for finish materials (like cabinets and flooring).  

We had 20 high net worth investors who placed equity and debt with us with a profit splitting arrangement.

If it has significant upside value, you should consider flipping that yourself or find a partner who knows what they are doing to flip it and split the profit.

Find out what they offer as far as education and support, what their fees/splits are and what their expectations might be.Remember, you will need a certain amount of continuing education hours, and you will want a Brokerage that has the support you need to help you through your contracts and answer questions.

Typically they have a side entrance that leads to the basement which can be easily split up with a door/wall.

For a partnership where you're providing all labor and the broker is funding the deal, a fair split typically ranges from 30-50% for you and 50-70% for the broker, depending on the value and complexity of your labor versus the financial risk they're taking.