If you remove the Glow Plugs there is a reamer to get the carbon out of the glow plug holes or if you look in: Fast navigation
http://www.peachparts.com/shopforum/diy-links-parts-category/146034-fast-navigation-do-yourself-links.html
I believe you will find alternative ways to get the carbon out. There is also a quick check to see if the Glow Plug resistance is what it is supposed to be but you need a Volt/Ohm meter.
However, that is not the definitive test for the pencil type glow plugs.
Bosch Glow Plugs (made in France or Germany not India) are entirely adequate and not expensive if you shop online. My way of thinking is that if you bought 4 of them and it turned out you did not need them it is not a waste to have extras on hand.
Having to buy a single Glow Plug locally could cost you as much as 3X the online price of one Plug.
However, the Injectors cost a lot more so deal with the Glow Plugs first.
As previously mentioned fix one of the issues then test. If you fix more then one thing at a time you won't know which fix to credit for the cure.
You probably know this but I am going to say it anyway. When the Glow Plug Light goes out you just keep the Key in the preglow position and you can continue to heat them till you hear the Timer Click and turn them off and then start. You can ever turn the Key off and back to the preglow position and start a whole new glow plug heating cycle.