I did a mix of hard money loan and 0% business credit cards.

This is a time consuming business.

Plus, if they're THAT good, why aren't they raking in the big bucks from doing the business on their own?

Here are some financing options to consider:HELOC or Cash-Out Refi on Another Property – If you or your mom have equity elsewhere, this could be a more flexible and lower-interest option.Business Line of Credit – Since the property is in an LLC, you might qualify for a business LOC, which could cover construction costs.Private Money Lender – If you’re okay with 12-15% rates, a private lender could fund this as a short-term loan, especially if the guesthouse will generate strong income.Construction Loan – Some lenders offer short-term construction financing, which converts to a longer-term mortgage once completed.Seller/Partner Financing – Bringing in an investor or structuring a joint venture with someone willing to fund the build in exchange for a share of the income.Credit Card Stacking or Unsecured Business Loans – Riskier but could work if you need to bridge a gap until the unit starts cash flowing.Would love to hear more details—especially your timeline and expected rental income.

The similarities are strong with the brothers with their behaviors, such as, suspending distributions to investors and other poor business practices.

Don't quote me on that, but it's easy to look up the IRS regulations.I recently had a conversation with somebody else who is planning to start an STR business. 

., They will be instrumental to your business. 

I normally advise that people start a business as a sole propeitor in their first year.If it is successful and something you want to continue, then have a conversation regarding entities.

Maybe I could leverage my other business but I don’t know the requirements for that as we do have outstanding loans already 

So pick an industry or business type you like, and I'd go talk to the businesses, ask them who their broker was, how was their experience with them and if they "specialized" in that industry.