I'm going for the ''Clean Hands'' ''Shadow'' and ''Ghost'' trophies all in one go, but as I'm going through the story, I've come across a bit of a problem.

I've just met Granny Rags, and she wants me to deal with the men knocking the door downstairs. The fact is, I can't without being seen straight away. Is there any way to deal with them quietly? Or should I just give up this optional objective and carry on with the main one?

Here's a similar topic and people's responses.

http://www.gamesas.com/topic/1416523-gentleman-callers-not-seen-question/

Be sure to do AT LEAST the first part.... I skipped Granny, and this locked me out
of an achievement at a much later point.

What do you mean the first part?

Finish the "gentleman callers" part, and she will ask you to do something else for her....

YES THERE IS! http://youtu.be/Hr_7wN-SKuc?hd=1!

( http://youtu.be/Hr_7wN-SKuc?hd=1 )
The fact is, you can deal with them without being seen straight away, you just need to use your imagination, so please watch the video above.

Did that help or?

You could blink up to the "roof bridge" on the other side, shooting sleeping darts on them from behind, and you will be too far away for them to see you.

That said, not doing any side quests make ''Clean Hands'' ''Shadow'' and ''Ghost'' a bit easier later on, cause then you're locked out from a certain thing later in the game.

Thanks for the info!

I've decided to start the game again, with the guidance of THE RED DRAGON'S walkthrough