Exploring the Shattered Matrix

First off, cool idea!

These are minor effects so have at most an area of 1 person for 1 round but can be maintained with an action each round. So the basic idea I use is 6 ft cubic. This translates into a disk of of fog 10' radius 1' deep. Skeeve and Gardakhan can work together to double this but that only ups it to 15' radius.

Now this is all mechanics of how I view it but this system is designed for flexibility so you can try and thin it out further to increase the area or change the effect.
Ex: If Gardakhan creates a 3 inch covering of mist over the ground it would have a radius of 30' and might show things walking but spider have thin legs so .... That is just how I see it but it would definitely help vs just looking around.

As a variant he could have a dust spirit make the surroundings very dusty so that foot falls would create a puff and leave obvious tracks. Again the problem with tiny spider feet.

The invisibility is a higher power spell (think a tier 2 ability that you could have access to with a 2nd magic/shaman trait) so totally countering it at your current power is tough.

That said, all of which is just to explain my thought process, I like to encourage and reward creative solutions so thinking like this is definitely a good thing and will help you characters in the story. Minor effects applied creatively like this can be very useful and fun