It’s a well-known fact that gamers like to be unique (some to the point of making it an issue), and yet in almost every game there is at least some overlap in terms of the skills and capabilities of the PCs in the party. So how do you make sure players with at least some identical mechanics still feel unique and needed at the table?
Any system with a teamwork mechanic is a good starting point. Systems like Fate, D&D, Pathfinder and Eclipse Phase all allow multiple characters with the same skill or focus area to collaborate on a single check, often with a primary specialist being chosen and everyone else granting either a passive or active bonus to their attempt.
While useful as a starting point, teamwork mechanics can start to turn stale quickly, especially if the same character is always acting as the primary specialist. Finding excuses in character backstories (or simply adding a house rule on teamwork rolls) to force players to pass the baton as far as who the primary is can make teamwork a more interesting exercise when there’s overlap since everyone gets a turn in the spotlight.
A different issue can arise in the case of ubiquitous skills, like perception or stealth. Typically, everyone has these skills at some value whether they put points in them or not, and everyone will be called on to roll them when the situation requires it.
This often means those who invested in the skill will either be the only ones to succeed, or will beat the difficulty by such a high margin that any nuance between relatively high performers is completely lost. In the former case, this may quickly negate the point of having the whole party roll when the specialists tell everyone what they spotted, or when one of the non-specialists getting spotted leads to combat that negates the specialists’ success in sneaking past.
In these cases, it can be worthwhile to set requirements on the roll. “Roll me Perception if you have at least seven ranks,” for instance. Alternatively, let your players divide the size of their successes between their less adept party members.
In Fate, if your professional ghost scores five shifts, let them gift a shift to other party members who fell short. In d20 systems, translate shifts to blocks of 5 points, so a rogue who needs a 15 but rolls a 31 can gift 3 other players a +5 bonus on their roll. For d100 systems, this might be -10 to the roller’s success for a +10 to their ally’s target number.
Whatever the mechanic, make sure the total needed for the party to succeed would still likely require 2-3 specialists, thus ensuring multiple sneakers still all feel valued.
Alternatively, don’t think of success on a given check like a ladder, but like a puzzle with different sized pieces. Your unskilled PCs share a tiny piece, but your specialists each unlock something different – and, critically, pieces that don’t automatically include one another.
Your PCs are stalking through the forest at night. The unskilled rollers notice rustling in the woods nearby. The first skilled PC rolls far better and notices the shape and type of creature prowling about in the woods. The second skilled PC notices a different type of prowler, hanging back, waiting on the smaller predators to weaken the PCs before it rushes in for the kill.
While all the different clues are related (you’re not alone and something is about to pounce on you), each noticer notices something different, and in the case of your specialists (or at least those with the highest totals), they each noticed something different. If either of them were missing, the party would be absent a very critical piece of information, which again makes sure they feel valued even though they’re both using the same skill in the same situation.
The last and perhaps most enjoyable method is to specifically design around the fact that you have specialty redundancy.
Create challenges that require splitting the party into specialized and non-specialized groups (say, creating a need for a small, stealthy group while giving the remaining group a different, concurrent task elsewhere that utilizes different skills), or into groups who each need a specialist (if you have two bring down two different technological systems at the same time, both engineers may need an escort from the more combat-ready PCs to two different locations).
Splitting the party specifically around redundant specialties can make players genuinely grateful for not being unique and encourage a little friendly competition between PCs who share a specialty. It may even highly the subtle differences in the execution of that specialty or other neighboring skills the PCs don’t have in common to create a more unique gestalt around the common skill.
Whatever way you do it, remember that redundancy can be a good thing in any type of PC, but it may be tricky to convince your players of that. Keep your challenges from being one-dimensional, and you’ll have no problem making room for more than one specialist at the table.