My tenant just told me that he wants his fiance and their one year old child to move in with him in a few weeks.

Then they took over your child's education with public schools.

Renting to college kids will give one direction to go ( 9 months of click click click), renting to mostly boomers another(think US Mail). 

If you have the resources to invest in a short-term rental, there's no way that your child is going to qualify for any governmental financial aid, no matter how hard you try to cook the books.  

We have a young family (one child) and are looking to make our money work for us rather than just waiting until retirement.Opportunity (and where I could use advice):I came across a social media post from a former high school classmate—now a loan consultant—who was seeking investors for potential flip or BRRRR projects.

I also have my first child on the way due in about a month so I am considering if I want to take on the work of furnishing the unit, marketing it, and generally learning something new while I am learning to be a dad.

The beneficiary would be your family, I.e a child or whoever the trust is essentially for at the end of day, and the trustee yourself.  

You can also pay your child out of the rental property as opposed to the LLC.

I'd wanted to just keep him because I just had my first child and don't really want to do a reno right now which the apartment does kinda need.

I went through this learning curve with our red-headed step child property.