Can very very few photons form the EMWs? One maybe interesting question please!
In quantum point of view, the electromagnetic waves (EMWs) consist of photons. However, if there are only very very few photons, can they form a wave-like macro EM field? 
OR
If a spherical monochromatic EMW (frequency is $\nu$) propagates and decays into very low level of energy flux density, e.g., for every square meter, the energy flux is far less than  1*$h\nu$ per second, then, does the EM fields still exist there?
OR
If the EMW is extremely weak (by value of corresponding energy flux density), can the electric field and magnetic field still exist in the spacetime and still propagate in the shape of waves? Or, in this case, is the form of wave only meaning the quantum wave function to indicate the probability of where the photons appear?
Thank you very much!
 A: The smallest EM wave is generated by single electrons in atoms and has discrete energy levels, which we can call a photon. This small EM wave tends to propagate in one direction where its E and M fields are strongest, the solution to Maxwell's equation says the E and M fields are well confined to sinusoids in a certain direction. However the wave function is a different function for the photon and it describes a probablilty nature so that the photon has a small chance of being anywhere but the greatest chance of going in a straight direction.  So for Q1 a few photons do form a field but localized, but for Q2 and Q3 I am not an expert but would say that the QM photon description is not the same as the Maxwell EM field, so the EM field is not measurable everywhere but QM says it possible.
A: This has been studied experimentally, how one photon at a time builds up the interference pattern that classical electromagnetic wave models perfectly.


Single-photon camera recording of photons from a double slit illuminated by very weak laser light. Left to right: single frame, superposition of 200, 1’000, and 500’000 frames.

The little dots clear on the left are the footprints of the photons as they interact with the camera's recording surface. The photons is posited as an elementary particle in the standard model of particle physics, and are called particles because of the point interaction with matter , like a classical particle.
They are in reality quantum mechanical entities building up interference patterns in space and time, not seen in classical particles. As the number of photons increases towards the right, the interference of the classical beam becomes clear. The same plots have been measured  for electrons .

However, if there are only very very few photons, can they form a wave-like macro EM field?

No, photons are localized, (within the Heisenberg uncertainty principle)  as seen above. They do not have an electromagnetic field in real spacetime, though their complex  wavefunction carries the information.
As you see , single photons are points, not spread over space-time

If a spherical monochromatic EMW (frequency is ν) propagates and decays into very low level of energy flux density, e.g., for every square meter, the energy flux is far less than 1*hν per second, then, does the EM fields still exist there?

No, there are only single photons as seen above

is the form of wave only meaning the quantum wave function to indicate the probability of where the photons appear?

The wave nature of the photon is in the wavefunction description, as modeled , for example,here

so it is just probabilities.
How in quantum field theory single photons bbuild up by superposition of their wavefucntions the classical wave is explored here , but a mathematics background in quantum field theory is necessary to understand it.
A: Here is a point which may make things clearer for you. 
The practical answer to your question depends strongly on the particular wavelength of the electromagnetic wave you are interested in. This is because (as you mention) an electromagnetic disturbance can be modeled either as the emission of photons or waves. The wave model is most convenient for dealing with wavelengths longer than infrared and the photon picture is most convenient for dealing with wavelengths shorter than that. 
Knowing that the energy of a photon E is equal to hc/lambda, big lambda means little E. 
For example, a radio frequency source at a wavelength of 3 meters (100mHz) produces photons of ~4 x 10^-7 eV, which is tiny on a per-photon basis. Note that a typical 100mHz FM radio station will be broadcasting anywhere from 50,000 watts to 250,000 watts of RF power; in this wavelength regime, then, it is customary to deal with the wave picture. 
When the energy per photon is of order ~1eV, the photon picture becomes more convenient. 
