Planting booboo

Recently planted out broccoli and brussels from root trainers. Was late evening, and I was in a hurry. All are growing well, but on close inspection I think I must have plated two seeds per station! So, I don't think digging them up and trying to separate them is an option.
 Obviously, I can't leave them like this so, can I just cut the weaker specimen off at the base?

Also, something is nibbling leaves. Looked on the back, and on one, I found what looked like minute 'granules'....almost powder. What might this be please.
Ta

could be some sort of fungus... what colour are the granules?  any chance of a pic or two?

butterfly eggs?