You are kind of conflating two problems if you have a parasitic drain thats one problem if you have a idea what it is disable that item or leg (pull the bulb or the fuse) This will stop the battery drain. As long as the item is not part of the running circuit cut it out and don't worry about it for now.

Then go back to my previous comment and determine if it is spark or fuel. If you don't you will be running in circles instead of narrowing the problem. If you have the manual there is a diagnosis tic flow chart to follow.

There are many reasons why a engine won't start but it starts. If it cranks and has compression then you look at fuel and spark (as said before)

If no fuel you look at pump, or the fuel injection system (but you don't know)

Spark ECM, Timing belt, crank sensor, ect (but you don't know)