However, my bank teller told me that an app or website deposit software may not be checking the signatures as diligently as a human teller, which means that the check could still get deposited into one tenant's account without all signatures. 

It's human nature (I call it lack of respect of others time).  

First of all, let us note that he is taller than a human should be allowed to be.

A banker made an absurd statement that you cannot buy a piece of real estate with these types of funds if you are going to benefit from buying said real estate because you are going to use the building for storage or in any way that you would benefit from.  

There's no human person ownership in any entity.

@Jay Rogers sorry, I have to add because it's a more absurd deal the more I think about it.

However, while 50% may be too conservative in high rent markets, it is not totally absurd neither.

2) Am I allowed to pay the same human a fee once we close a contract on said home?

And it's OK, to have been a hero when needed and than back to just regular ordinary human there after, what they did was still great and does not change because later they wander the streets in a robe saying "hey, pull my finger" (do your research on Benjamín Franklin, it's actually an analogy not that far from reality, just add some STD's, lol). 

This seems almost absurd in today's market.