It’s a rural river front property and main highway exposure is Airbnb a good option?

I have a few others on my list but all of the OH metro's keep rising to the top of the list is cashflow is your main goal. 

So I talked to him yesterday, mainly to see if that would still be a problem.

For estate planning purposes I want the both of us to be members of he LLC.

Hard money lenders many times will let you invest in their short term debt.. ( these are commercial purpose)One thing I get a lot of is direct mail.. its exactly the same method that real estate wholesalers use.they search public records.. get lists of private owners of notes.. ( usually the target is a seller carry back) and then they blast out direct mail offering to buy the note from the current note holder.. the pitch in 99% of those is all the same  same buzz words..

I am purchasing duplex, just found out after the home inspection it needs a new main water line as the old one is galvanized steel and is affecting the water pressure drastically.

Is the purpose of this to keep folks depending on, say their fixed w-2 income to qualify rather than rental income? 

If you can show that was the purpose of the property and hold it over a year a 1031 may become a possibility. 

Can ABC LLC continue to be the main contact on behalf of the new Investor?

As a general rule, you want to use an S-corporation.While liability concerns are an issue, that is not the main reason I am saying to use an S-corporation.