SOHK does have some pretty good rules for people working together.. You all can look them up; but here are some.
Smallest skill bonus in the group
+ Leader's Skill Rank
- # in group
+ Leader's Ranks in Leadership
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The Leader can also split their own Skill Rank bonus among any people in the group they want. This can temporarily increase the individual's skill; adding to the group bonus.
To the last line about Leader's Ranks in Leadership, I would add, Flora/Fauna (Water) Lore, maybe Region Lore, Cooking (can stretch rations so there are mor eot go around), etc.
Now the Skill does have difficulties for different climates/terrains. One person takes 4 hours to forage so that
they can survive. Each additional person raises the difficulty by one!
So to use the Coordinated Effort rules above, I wouldn't lower the difficulty (more mouths to feed and all). I would just modify the chance to actually find enough to food/water to
survive. Eating raw or even fire cooked wild onions will make you pretty darn gassy. Gleefully gobbling up a handfull of minnows or grubs, won't help your standing with those ladies in waiting who lost their way in the forest. You definitely won't gain weight eating like this, but the skill says that you may survive.