Advice re candling eggs

Hello
I have a broody with 6 eggs under her , she has been sitting on them for 8 days now.  I candled them at 6 days and am pretty sure 2 are non fertile - they look pretty well clear. I gather it would be a good idea to remove these as early as possible.  I'm just frightened of getting it wrong. 
I will candle again tonight - I think I just need reassureance that if an egg is clear at 8 days its better to remove it.  Is there any other way of telling fertility?
As for the other 4 - 2 I'm unsure and 2 I definitely saw movement  .
Any help gratefully received!
 

Thanks for your advice - I have been looking at eggs by shining a light through the side.  I will shine it through the bottom (with pointy end up?) as you have suggested.  This will require a slight modification to my candler (mobile phone torch and toilet roll)!

Thanks again - got rid of the 2 that looked like duds - I broke them open and they were indeed duds - thank god!
I have 3 that are definitely moving  but 1 that just looks like a dark mass.  I'm not sure enough to remove it can I leave it in there just incase or will it infect the other eggs if it is bad?