The last method seems to be the most practical for me if I can just get the right deal and makes the most financial sense to reduce my overall expenses in the long-term.

The last financial advisor told me securities based loans are close to a conventional loan's rate.

Sounds like she may have financial problems or is anticipating something popping up in the future

It may also be helpful to consult with a real estate attorney or financial advisor for guidance.

It's best to consult with a real estate attorney or financial advisor to understand all your options and potential implications.

Validate your financial metrics again. 

That said, it is a financial decision first and foremost.

I told them per the Homeowners Protection Act of 1998 they are obligated to automatically drop the PMI when my loan reached 78% LTV and I wanted to be reimbursed for the (26) PMI payments I made past that point. 

However, as time went on, I found that the passive income generated from my rental property allowed me to achieve financial stability and freedom.

In this case your Mother-in-law suite will need a 1-hour rated ceiling, assuming it supports the fire rated wall above, to completely protect it from the dwelling unit you intend to use an as an Airbnb.