Do you allow additions or outbuildings? 

Or, there must be a loophole which allow constructing duplexes in certain way under A1 Fam dwelling which I don't know about. any thoughts? 

I usually give $1 earnest money deposit to the seller to secure the property and allow me to do my due diligence. 

The lender is not allowed to charge you $1 more than the title company charges. 

But an LLC Ira and Solo IRA will allow me to make my own deals, sign my own checks without having to go through someone else doing that work.

No sense in looking for construction loans if the city is not going to allow you to build what you'd like to build there ...

Secondly, am I allowed to get a 2nd loan along with this loan assumption?

The Solo option allows you to be tax deferrable and in most instances you can with manage it yourself with checkbook writing or through some companies like Fidelity, they require a TPA/Custodian to help manage the documents for REI & things.

People are getting greedy, and agents are allowing it to happen.

This is different than your situation because we are building a business together whereas you might just be partnering this one time.In your situation you should still consider allowing your "partners" to share in the profit, but on a much smaller scale.