Only one person can make a check at any given time. This avoids each player at the table making a check until someone gets a number they like. That said, there is a way to improve the odds of the person making the check.
Aiding a Check
A player wanting to help someone make a check must make a DC 12 check with the assigned skill. If they make the check, the person they are helping gains +2 to their roll. However, if they fail, the person making the check gets a -1 to their check. This can be stacked.
For example, Sam wants to make a perception check. Three people elect to help him with the check. They each make the DC 12 Perception check. Two succeed, and one fails. So Sam gets to make his Perception check with a +3 bonus to his existing modifiers.
Failing a Check
Since only being allowed to make a check once could lead to some sudden dead ends when picking a lock. If someone fails at picking a lock with thieves' tools, they will not be able to try again until they gain another level. This forces the party to look for a key or attempt to break a door down. The DC to break a door is generally (some doors are made of stronger material) the same DC as picking the lock +3. Again, it can only be attempted once.
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