Will crank no start

I have a 3.6l ly7 motor. Occasional backfire in which white smoke comes out of the air intake. Opened intake just to get a visual confirmation of where the smoke was coming from. Found oil residue in the hose from air filter to mass air flow sensor. Had been getting random misfire codes on all cylinders periodically. At first the car started making like a violent popping/snapping noise that you could really feel. Seems as if it was coming from virtually the center of the car just toward center from the gas pedal region. Being on a low maintenance budget having 3 kids and being a young family we tried to wait as long as possible to address the problem but it worsened over time and the pops were so harsh it sounds like two gears slipping past each other and shearing of a tooth or something. Eventually it started popping between gears even when just coasting on a flat road. The only solution is to not touch the gas pedal when it starts. My wife drove it last up a hard inclined Hwy and made it to the top of the hill will a couple violent pops only for the car to shut off having been able to start it since. Now when it turns over it sounds almost as if the battery is drained and isn't providing enough cranking amps and backfires doesn't sound like its even trying to start. Really need this car up and going. Not sure if I need to be looking towards possible timing kit or what to do?