Anna, Sorry but its either a group resource (e.g. "electricians" at XXX% representing the number of electricians in the group), or it's individual resources (e.g. Joe, Linda, Jack, etc.).

The best you can do with a group resource is to set up a calendar representing time off that is common to all members (e.g. holidays). With individual resources you can of course identify individual time off periods in their resource calendar (e.g. vacation, sick, etc.).

So, if you want/need to track who's available when, you will need to use individual resources and assign them individually to tasks. Remember, you can still use Project's leveling feature to help alleviate overallocation.