CCSet in cocos2d-x don't have methods to join two sets or remove objects from one set in another. You can use touch delegate instead of standard delegate and use methods:
virtual bool ccTouchBegan (CCTouch *pTouch, CCEvent *pEvent);
virtual bool ccTouchMoved (CCTouch *pTouch, CCEvent *pEvent);
virtual void ccTouchEnded (CCTouch *pTouch, CCEvent *pEvent);
Then you can add or remove every single touch from or to _touches.
If you want use touch delegate you must override registerWithTouchDispatcher();
void Strona::registerWithTouchDispatcher() {
CCDirector::sharedDirector()->getTouchDispatcher()->addTargetedDelegate(this, this->getTouchPriority(), true);
}
Or you can simply iterate in every touch in touches from ccTouchesBegan and add every touch from touches to _touches.