Is QM something that belongs to all relative small particles or only to subatomic particles? For us human beings subatomic particles like elektrons are described by the laws of QM. But imagine their is a very huge giant looking on the universe. For him all the planets and stars are so tiny like elektrons are for us. Is it possible that at that level you also need QM laws or is qm just reserved for subatomic particles as it is only for them an intristic 'property'? I know a little bit a philisophical question but how would theoretical phycisists answer this question?
 A: A meter is always a meter, and a planckmeter is always a planckmeter - no matter how big you are. The effective regime of QM is always on atomic scale, so you would not need it to describe the motion of a planet even if you happen to be so big that the size of a planet compared to yours would be like the size of an elementary particle compared to us.
A: I believe that the separation between "classical" physics and quantum mechanics somewhat complicates learning, at least at the master level physics. In fact, many macroscopic effects can be well described by the formalism usually reserved for QM (e.g. wave diffraction, Gouy shift). 
Some other macroscopic phenomena completely rely on QM to be explained (e.g. semi- and super-conductors); moreover using the proper QM can provide insight and motivation for a student.
So the very premise of the question is unrealistic. QM is the correct framework of physical description of reality even at our, human, level of dimensions. 
A: Scale is certainly important when you're thinking about the appropriate type of dynamics to use to describe a system.  Newtonian mechanics, which is known to be incomplete, is typically very accurate for macroscopic objects (i.e. plannets), when they are not moving at near light speeds (i.e. relativistic corrections are very small).  Typically, quantum mechanics is used to describe the behavior of one, or a very limited number of particles.  When discussing things like shining stars, which do rely on quantum effects of many, many particles, you are in the domain of what is usually called statistical mechanics.  
A: Until demonstrated otherwise, it is both logical and prudent to assume that the laws surrounding QM apply equally at both micro and macro scales, the difference being that a single photon in a Double Slit experiment has a great number of possible paths to take (evidenced by the interference pattern), while the sum of the trillions upon trillions of quantum events that make up a planet (say Jupiter) have but one exceedingly likely outcome (for all intents and purposes one option with 100% probability), and that is to be a gas giant in orbit around the Sun.
There have been and continue to be many handwaving explanations that QM has no place on the scale of our day to day life and beyond, but I have yet to read any that does not reduce to "It doesn't, because I said so".
A: "a very huge giant looking on the universe. For him all the planets and stars are so tiny like electrons are for us". 
Well that means the huge giant can not see planets with its naked eyes and needs planet size photons to see planet sized electrons. Obviously the uncertainty principle will hold good because just by the process of seeing, the planets will be thrown away from where they were supposed to be (if they are not destroyed by bombardment of the planet sized photons). Moreover, planet sized photons can not travel at speed of our photons. 
Philosophically, the question can be put the other way round - will a tiny being (to whom electrons look like planets) see no QM in subatomic particles? But we know that the interference pattern is not going away irrespective of which being is looking at it. Also, photons of tiny being have to be much smaller, and faster as compared to our photons otherwise the tiny being can not see our photons from behind. (violation of relativity)
QM does not appear to be relative because to be relative, it has to violate relativity. 
May be that is why we have not been able to merge QM and relativity.
I am no physicist to say "we have not been able to merge QM and relativity". I said that because I have seen this in youtube documentaries.
