Properties of entanglement between particles

Oct 2017
What determines the formation of entanglement between two particles? Is it just a distance between two particles which have not yet conferred a state/spin?
Pair production is the main one. I don't know anything about the other methods, but apparently there are other methods.

I read online that different types of particles like photon and electron could become entangled. Is this true?
Can one particle be entangled to only one or two or more other particles?
Yep, but I don't know anything about it!

Could entangled particles be unentangled?
What if one photon that undertook a state becomes absorbed and its energy converted. What will happen to its previously entangled counterpart, will it lose state and return to a wavefunction?
Entangled particles behave like a single system, so absorption of one photon is actually a partial absorption of the whole. I don't know what that would look like.