Generally, you always want to over-prepare someone for a quest. This way, if they do manage it to do it with less people than specified they feel a sense of accomplishment and if they failed they will understand the reason why they failed.
If you under-prepare people to the difficulty of a quest, they will feel frustrated and QQ alot more if they fail to accomplish it with the specified amount of people.
what what what? did u even read the OP? ><