I heard that less than 20% down causes additional insurance fee? 

This practice also frees up more money for lenders to use to fund additional mortgages.In "non-conforming loan" world, anything goes.

Unless the borrower is self employed and takes a lot of expenses to show lower income on their returns then it usually makes sense to pay a couple thousand a year in higher interest (you can pay like 4,000 a year in additional interest for DSCR if you are saving 30+k on your tax bill kind of math lol)

In addition to interest and repairs, you can deduct off a 27 year depreciation on the home. 

Purchasing the LLC gives you ownership of the property, but it also opens you up to additional legal exposure since the entity has been active, and there is no way to really know for sure what else they used the LLC for.

In addition, when you have leverage you have the other benefits which @Ali Boone mention.

If you are looking to refinance the rate and aren't concerned with taking additional equity out on your property, then you should use a rate/term refinance.

Feedback has not suggested property needs additional repairs/work, only that they are looking in a different area.

Additionally, your brother would inherit your cost basis in the property, which could result in significant capital gains tax if he sells the property later.

If they have money and can compete on pricing, brokers will be the best bet.