There will be big pressure on rents over the next year or two in Austin area due to the vast number of apartments coming online. 

You could monitor the power usage for the two units using this device then pass through the correct billing. https://www.amazon.com/gp/prod... 

But I plan on adding a 40/60 split on the next lease renewal between the two units. 

Saying yes to their request can/will put you in the middle of any financial disagreements between the two of them.

You are thinking you will have one month vacancy every two years.

I want to rent them out separately and wondering if I’m able to just add a mailbox and label each door as ‘A’ and ‘B’ Also, how do you separate electricity/utility bills for each tenant?

I’m newer to real estate investing, hoping to buy one of my first properties in the next month or two.

(I'm personally happy this failed because I have two clients under contract on homes they plan to short-term rent -- one in the mountains outside of Colorado Springs and the other right near Breckenridge.) 

There are two different issues at play - the titling and ownership of everything is more of a legal liability issue.It is possible to still have a tax partnership just with execution of a JV agreement, even if there is no formal LLC in place. 

What you are asking the title company to do is close on the first purchase without funding then close the second deal which will payoff the seller in property deal one and you in property deal two.