This is a substance of the transaction vs. structure issue. 

Wonder if anyone has run into the issue I'm havingMy wife and her parents went in on a duplex together and the three of them are all on the title and loan.My wife and I are in escrow on a house in Citrus Heights.

Finally a fixed fee could work, but same underlying issue exist which is getting an accurate estimate of their consumption.I understand they're perspective, but I just feel like the tenant is just trying to cut corners.

That's a common thing that appeals to out of state investors I think.. 

It sounds like a communication issue. 

A few important things I would be looking for:1) the experience and credentials of the broker who supervises the company as well as the lead property manager2) the services they offer and how they line up with your needs and expectations3) the use of technology to make their job and yours easier 4) if they have a landlord-tenant attorney on retainer to help guide them on legal issues (not to mention the creation of lease agreement, landlord forms and notices, etc.)5) their process and policy for a) listing, b) application, c) tenant selection, d) routine inspections, e) maintenance services, f) property and tenancy update reports to you, g) lease enforcement policy, and f) move-out process.6) property owner reviews (you can't always rely on Google reviews, because they may not reflect actual quality of the company, but still) 7) beneficial programs for both owner and tenant 8) a property management agreement that would indicate they know what they're doing and have the experience to know what matters in a PMA.

You may look for a "pre-fab" countertop supplier who sells half slabs (perfect for counters and already fabricated.Look on Pinterest for a little inspiration and start collecting ideas, then see the common look that you gravitate towards.If you'd like to hop on a call, I'd be happy to help with some pointers.

Because my issue is that since I bought the property this 15th they will be paying for may but I would like to have them start paying the rent for the month forward.

But, a couple issues come to mind:After co-mingling funds, I believe the next "common way" to pierce your corporate veil is to use the LLC as an alter-ego. 

@Derrick Wallace Conflating "having a business" with "having a business entity" is very common.