Being able to see a bird every 20 minutes in a couple hours span is quite indicative of the fact that there were likely more in the area that covered their er "ass end" really well and successfully allowed you to walk past!
First off all (and I mention this cause even experienced folks may be caught unaware in the heat of sudden excitement), muzzle control is paramount when 2-3 guns are walking the same logging trail.
At this time of the season, with thick vegetation creeping well into the trails, it pays to always watch the edges at ground level in front of you. On a fairly straight path, this may be achieved out to a good distance as you walk forward. The other guys could cover the flanks observing the terrain/cover, eyeing fallen logs, low level branches and up into the trees etc.
In dry conditions, with leaves on the ground, one would eventually come to recognize the tell tale crunching noise if a bird is moving inside the bushes – one may note, Squirrels foraging on the ground make similar noises although the movement will seem more like abrupt hop/skip maneuver. The noise made by a Grouse walking over dry leaves is more consistent.
Always assume, a bird when spotted retreating into the bush will initially use various evading tactics (while remaining on the ground) for quite some time until it feels too threatened. It may hold or simply choose to bolt. As already suggested, apply the move/pause procedure to prompt a flush.
Where possible, take the shot despite the leaves/limbs etc (remember to follow through). I must state, retrieval without the benefit of a bird dog will usually be a challenge in the Grouse bush.
Lastly, a double gun equipped with open/tight chokes combo and double triggers will always offer an edge via ability of instant choke selection.