We offered 407 and asked for closing costs.

It depends on what you want to invest in.

-Transfer the property into an LLC – This may allow me to take ownership while potentially avoiding property tax reassessment, however this sounds like an involved process-Establish a living trust for my aunt and mother – The trust would specify that I inherit the property upon their passing and provide step up in cost basis but i'm worried that the living trust can be modified to have me removed (who knows what can happen) - My mother is somewhat volatile.I would like to live in the property and my mother will live in her second property with her husband. 

., to 2.5x or 2.75x) since tenants won’t have additional out-of-pocket utility costs.

Multiple people including myself have tried to caution him of the the true costs but he's been repeatedly dismissive and has made it clear we give him motivation and he wants to prove us all wrong (whatever that means). 

I am slightly confused about your numbers, though...is the $215/SF the construction cost? 

Sounds like you need to have a relationship with a couple of good contractors, 40k for vinyl siding sounds high, what was the material cost.  

We then will either sell or keep it as a STR depending on what makes more sense for us. 

Quote from @Erick Pena: A "good" rental property is one that covers all expenses (mortgage, taxes, insurance, maintenance, property management fees, and any other costs) and still leave a surplus (commonly referred to as cash flow).Calculate cash flow as: Cash Flow = Rental Income − Operating Expenses − DebtThere's much more to it, but that's the basic idea.

Today it has good cash flow (~$6k/month using 49% expense ratio) and is up ~$1m above costs.