Even if they only appreciate flat with inflation, renting doesn’t appreciate at all.

Using a percentage for capex is flat wrong, because a new water heater costs the same, regardless if your rent is $600 or $1600.

There is also a flat fee portion of the bill which is split 50/50.

I find it completely unethical, spiteful, and flat out disgusting to use this crisis and rent freeze to their advantage when it's intended for those who have lost their source of income and/or are dealing with life and death with themselves or their loved ones.

Everyone should theoretically be approved so why are people not going to be able to pay mortgage payments unless they just flat out dont apply for unemployment? 

I suppose if you're including utilities in their rent pricing, it makes a bit more sense, but from my experience, it's easier to find a tenant if you have a flat rent rate, then put the cost of the utilities right onto them.

Should I bill the tenants a flat rate per month?

I also have a 2 flat that is under a $100 every month.  

Meaning, if you had to liquidate your assets, you would have cash in excess of your debts.

That will create an excess of retail space and it will force rents down everywhere.