Hi @Shannon Moyer ,
I hope these answers help!
1. Since the money is coming out from an IRA, he should check with Merrill Lynch on the tax implications. The amount he can withdraw will depend on the type of IRA and his age (maybe other factors too). Merrill Lynch can probably also advice as to the easiest way to transfer the money. Perhaps he can just write a check?
2. The IRS will just look at your returns, so you'll just want to make sure you get the reporting right. You may look into hiring a CPA to prepare your returns.
3. Yes, splitting the proceeds is a good way to do it. In that case, your father-in-law is no loaning the money... you'd probably just consider him an equity investor. A loan comes with an interest rate and is paid before the equity holders get paid.
4. You probably don't need a lawyer on a small deal like this, provided you have a good, trusting relationship with your father-in-law and you don't want to do this through a business entity (like an LLC). You also don't "need" an accountant as the bookkeeping and as tax preparation for a single deal are not super difficult. However, if you want to focus on doing the work for this first deal, outsource the accounting would not be a bad idea (see #2).
5. You're asking good questions! Keep reading and learning.
I hope that helps. I wish you the best!