Hi Raj and Sowmya,

The issue with the Query provided is you cannot directly extract the users if the Queue contains Roles and Subordinate / Roles and Internal Subordinates.
/* Select UserOrGroupId From GroupMember where GroupId =:IdOfAboveQuery */
This(above) Query will not work if Queue has Roles and Subordinate added as a group in Queue. I think we need to firstly fetch the Role ID from the UserRole Object and then Query the User object with the provided roleId.

/*select Id from UserRole where ParentRoleId IN :roleIds AND ParentRoleID != null */
Please correct me if i'm Wrong.

I got a code from one of the blog posts as under.
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public static Set<id> GetUserIdsFromGroup(Set<Id> groupIds)
    {
        // store the results in a set so we don't get duplicates
        Set<Id> result=new Set<Id>();
        String userType = Schema.SObjectType.User.getKeyPrefix(); //005
        String groupType = Schema.SObjectType.Group.getKeyPrefix(); //00G
        Set<Id> groupIdProxys = new Set<Id>();
        // Loop through all group members in a group
        for(GroupMember m : [Select Id, UserOrGroupId, Group.Type, Group.RelatedId From GroupMember Where GroupId in :groupIds])
        {
            // If the user or group id is a user
            if(((String)m.UserOrGroupId).startsWith(userType))
            {
                result.add(m.UserOrGroupId);
            }
            // If the user or group id is a group
            // Note: there may be a problem with governor limits if this is called too many times
            else if (((String)m.UserOrGroupId).startsWith(groupType))
            {
                // Call this function again but pass in the group found within this group
                groupIdProxys.add(m.userOrGroupId);
                
            }
        }
        if(groupIdProxys.size() > 0)
        {    
            Set<id> groupId = new set<id>();
            Set<id> roleId = new set<id>();
            Set<id> roleAndSubId = new set<Id>();

            for(Group g2 : [Select Id, Type, relatedId From Group Where Id = :groupIdProxys]){
                if(g2.Type == 'Role'){  
                    roleId.add(g2.relatedId);    
                }
                else if(g2.Type== 'RoleAndSubordinates'){ 
                    roleAndSubId.add(g2.relatedId);            
                }                                            
                else if(g2.Type== 'PRMOrganization'){        
                    roleId.add(g2.relatedId);                            
                }
                else if(g2.Type== 'Regular'){
                    groupId.add(g2.id);    
                }
                system.debug(g2);
            }
            if(roleAndSubId.size()>0){
                roleId.addAll(getAllSubRoleIds(roleAndSubId));
            }
            if(roleId.size()>0){
                for(User u: [select id from user where UserRoleId IN: roleId]){
                    result.add(u.id);
                }
            }
            if(groupId.size()>0){
                for(GroupMember gm : [select id, UserOrGroupId from GroupMember where GroupId IN: groupId]){
                    result.add(gm.UserOrGroupId);        
                }
            }
        }
        return result;  
    }
    
    public static Set<ID> getAllSubRoleIds(Set<ID> roleIds) {
    
        Set<ID> currentRoleIds = new Set<ID>();
    
        // get all of the roles underneath the passed roles
        for(UserRole userRole :[select Id from UserRole where ParentRoleId IN :roleIds AND ParentRoleID != null limit 40000])
            currentRoleIds.add(userRole.Id);
    
        // go fetch some more rolls!
        if(currentRoleIds.size() > 0)
          currentRoleIds.addAll(getAllSubRoleIds(currentRoleIds));
    
        return currentRoleIds;
    
    }

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