If you're really uncomfortable trying to remove the final glow plug, then replace the two that you can, try to start the engine
and see if the results are satisfactory enough.
However, you shouldn't be afraid to break the fuel
systems' air tight integrity, there's really very little difference (in bleeding procedure at least) in loosening that banjo bolt and turning it, or removing the banjo bolt entirely, as may likely be the case.
The banjo bolt will turn if you just loosen it a little, it may give you enough clearance to remove the glowplug. There are copper washers on all sides of the banjos (there is a return banjo and a feed banjo, for what, if memory serves, is a total of three). To do the job 'properly' you should replace them when the fittings are loosened; I typically reuse them. If they don't leak, they're good. You should have some spares on board anyway, just in case...
If you can get the glowplug out with just loosening the fitting, it is be possible that the engine
will start without bleeding, and the small amount of air will work itself out through the system. It might even be possible if you have to remove the fittings, these little engines are very forgiving.
After fitting everything back up (don't overtighten), try it and see if she starts.
If not, there is a little lever on the lift
pump that can be used to reprime the system, or you can use a squeeze bulb like those found on outboards, ar you can get a electric fuel pump
from an autoparts store to speed things up. Any generic gas pump will work fine. Many people just leave them plumbed in to aid in filter changes and such. I just use a squeeze bulb, left plumbed in line after the tank but before the primary filter.
The one thing you need to be careful about is cleanliness, especially if you have to remove the banjo fittings. Clean the area well before you start, some WD40 or similar and compressed air is a good thing if you have it, otherwise a toothbrush or somesuch and diesel are good. Since the fittings are after the filters, there is a possibility of introducing dirt, which injection pumps really don't like. With a little care you shouldn't have a problem though; it is a common thing to do.
The black soot on the un-heating glowplugs is normal.
It is also important for quick starts to have fully charged batteries and good clean, corrosion
free connections on all terminals and between all grounding surfaces. Any place that is deficient in these points can result in slower than normal cranking speeds and thus slow starting.