Car has intermittent starting issues?

It started out as a possible gas issue when I first got gas one day and then it wouldn't start on first or second go and barely cranked over on the third. We have since replaced the fuel pump full send unit and still didn't fix the starting issue, then replaced battery with a new one. Still unresolved and the codes were showing a low voltage for EVAP, the only thing we can see wrong with EVAP is the control solenoid and doesn't appear affecting the starting. This is as far as we've been able to diagnose. Also, the car had an aftermarket sound system with box but has since been removed and all wires have been disconnected from system for over a year before the issue as of recent. So, the system has not been playing and the car has been fine up until 3 weeks or so now. It is my deceased brother's car that I am trying to take care of, so it means more than the world to me that I get it back on the road. I am in desperate need of advice. ~Cameron