Skill Checks

For something that 1 person would do (investigate, insight, etc.) choose person to perform. If others want to try also, grant the person advantage. Only 1 person does the check. If it fails the others would assume that they won’t work either. They know they tried and failed and now you need to look for an alternative solution.

There may be some situations or skills that it might make sense to have a 2nd person try. However, the DM may limit this based on the situation. Remember that the PC doesn't know that the first person rolled low.

In no situation should the same PC try the same check again unless they change their approach in a substantially different way.
Example: The rogue tries to to pick the lock with his lock picks but rolls a 5. The result is the Rogue is unable to pick the lock. Someone else might try (if the DM allows), or the party resorts to breaking the lock, casting knock, use a crowbar on the lock or find some other creative way to open the lock or the chest or door or whatever it is.

Additional Rambling (4/30/21):

A roll has to have a consequence or else why make it. If there is no chance of failure, then I'll just say "you succeed." If however we roll and fail you don't get to keep on trying the same thing until you succeed. Where it's reasonable I think a 2nd person trying may make sense maybe even a third. In some cases however the party should trust the first person who makes the role. For example, if a person rolls persuasion and fails, a 2nd person can't just roll the die unless they do something else significant to actually persuade. If a person looks for a trap and finds nothing, unless that person says, "I seem to be having issues, why don't you look" the rest of the party should trust there are no traps. Assume the character doesn't know what the player rolled. If he rolled a nat 20 would you double check his work?

Things like lock picking are going to be 1 try per person. If you fail, it means you can't pick it. Find another way to open the object.