Tere! :)
седую тучу - "a gray cloud" - I mean they've seen not the gray clouds (on the sky), but an enormous crowd of enemies :) So, it should be "a cloud" (singular) in the first case as well. (IMHO) ;)

Next: "Только мы видим" should not be understood literally.
And example from Pushkin:
"ТОЛЬКО вымолвить успела, дверь тихонько заскрипела..."
So the correct translation: "SUDDENLY we can see..." or "In that moment we see..."

Russian language is strange ;)