14.5 is good, the alternator is definitely charging the battery. 12.50 when off sounds like a good battery as well, how are you testing the drain? It could be a parasitic drain flattening it overnight but it would have to be fairly substantial to flatten it overnight. Get it drop tested but also measure the current draw when the car's in "sleep" mode (about 20 mins after engine off).
If you've not done this before you need a multimeter with amps mode - connect it in series with the battery terminal and DONT use anything (ie ignition / start / windows). You should see a few amps when you first connect it and then it should settle down - after 10 minutes it should be next to nothing and after 20 it should be almost zero.
Glowplugs, again you can test these - put the meter in resistance mode and measure the resistance between the block and the plugs electrical connector - ideally they should all be less then 1ohm and anything above indicates a plugs poor or failing.
