If you look at area 3 and 4.

Question 1 :There is a ogre adjecent to 2 stones, would the heroes be able to move digonaly across the stones on the "outer" sides?

Question 2: Where the 4x6 and the 4x4 map tile meets there is no space betwen them in the quest guide, but ther is irl there is a small gap, would these gap block line of sight or should they just be ignored?

1. Yes. Diagonal movement is never blocked by obstructions in the side spaces; if the square you're moving to is open, it's legal.

2. All map tiles have walls around all the edges, except where the connectors are. That means, for example, that the only way out of the central Start Area is through one of the four doors - you can't go "around" the doors even though the tiles are right next to each other, because there are walls there. The same reasoning applies to the meeting of the 4x4 and 4x6 tiles in areas 3 and 4 - you can go between them at the center two squares (where the connectors are), but the edge squares have walls blocking them, so you can't go directly between them.