Singleton class for mutex in c++

I am struggling tog et this working but it seems there is something I don't fully understand.

I have a multithread application in a single file (2 classes and the real main in which I crete threads and everything). I want to split in 3 files. One for each class (with their headers) and one for main.

I have a couple of mutex and a queue to share messages between threads and lock and unlock them at any time.

I want to write a singleton class so all of them can share the mutex:

header:

#ifndef COMMONSINGLETON_H
#define COMMONSINGLETON_H

#include <mutex>          // std::mutex
#include <queue>

class CommonSingleton{
    private:
        static std::mutex               mutex_w_b;
        //static std::mutex               mutex_wifi_ok;
        //static std::queue <std::string> queue_w_b;

    public:
        static CommonSingleton& getInstance();
        std::mutex GetMutexWB();
        //std::mutex GetMutexWiFiOk();
        //std::queue <std::string> GetQueueWB();
    private:
        CommonSingleton() {};
        CommonSingleton(CommonSingleton const&);
        void operator=(CommonSingleton const&);
};
#endif

And my .cpp file:

#include "commonsingleton.h"

static CommonSingleton& CommonSingleton::getInstance(){
    static CommonSingleton instance;
    return instance;
}
std::mutex CommonSingleton::GetMutexWB(){
    return mutex_w_b;
}
/*std::mutex CommonSingleton::GetMutexWiFiOk(){
    return mutex_wifi_ok;
}
std::queue <std::string> CommonSingleton::GetQueueWB(){
   return queue_w_b;
}*/

In my main I have this to test mutex:

CommonSingleton::getInstance().GetMutexWB.lock();

But now I have commented, just to figure out how to compile. This is the error I get:

commonsingleton.cpp:4:54: error: cannot declare member function ‘static 
CommonSingleton& CommonSingleton::getInstance()’ to have static linkage [-
fpermissive]
static CommonSingleton& CommonSingleton::getInstance(){
                                                  ^
commonsingleton.cpp: In member function ‘std::mutex 
CommonSingleton::GetMutexWB()’:
commonsingleton.cpp:9:12: error: use of deleted function 
‘std::mutex::mutex(const std::mutex&)’
return mutex_w_b;
            ^
In file included from commonsingleton.h:5:0,
from commonsingleton.cpp:1:
/usr/include/c++/4.8/mutex:128:5: error: declared here
mutex(const mutex&) = delete;

What am I doing wrong right here?