An ADU could rent for an additional $1,200–$2,000/month, depending on the local market, potentially doubling the property's cash flow.

There is no law against getting a second lien either fixed or as a HELOC in Texas (as many believe), as we do them every day.

All you need are local vendors you know...with texting and internet, and good tenants.  

I am breaking into real estate investing and have extensive experience in condo / townhome law and association laws.

I would be more concerned about the brother in law potentially moving out mid-lease and leaving the couple.

I haven't gotten serious yet and don't have a local agent, but I have been window shopping and may reach out.Hi @James Bing, yes I manage my own properties by leveraging technology & local relationships to automate the self managing process.

I understand Philadelphia requires a local property manager. 

In Houston, you can either invest locally or explore strong Texas markets like San Antonio (affordable duplexes, strong job market), DFW suburbs (duplex-friendly zoning, growing economy), or Houston suburbs (Spring, Cypress, The Woodlands for good schools and tenant demand).

If it is big enough that they could all fit in one side, then maybe she could still only charge her father-in-law $150/month and maybe rent out the other side to someone else.Her current house actually has a basement that could be finished into an apartment.

Your local laws are going to prevail.