I have come across several companies like Legal Zoom, Zen Business and many others, some which I think want to overcharged me.  

Or maybe your family business is property management ?

I work with some of the best in the business.

He wants to use the 50k to jumpstart fix and flip business 

In general though, you're able to directly offset your income from the active rental activity with the *losses* you take from the business, but once the business becomes profitable, this would also add to your taxable income. 

While demolition costs are nondeductible, a taxpayer may claim a loss deduction when the depreciable business property is retired from use in a trade or business or from use in the production of income.I would strongly advice talking with a real estate focused accountant here to help guide you.

People like to do business with people who do business, present a good deal, and you will have a long term buyer to work with!

@Courtney Olson I did this for my candle business but it could work for real estateMaybe offer Step Up  Payments too, as long as the number works, and hint at it helping wiht inflation and maybe combined it with an interest rate that is above typical inflation.A combo of something like 4% inflation to keep your same spending power as the years go, and we increase the payment by $25/month every 12 months so your spending power stays the same and you get a bit of a raise every year, then we could do a balloon payment in 10 years to settle the rest.Something like that could be an option. 

If you still owed $300,000 in 2019, you could have refinanced for under 4% interest and your payment would be less than half what it currently is.I recommend you study the market and figure out what your home is really worth as a rental, then charge accordingly.

Have a business relationship with the owner of the land How did you finance this deal?