How are demons able to come to this world?
They can "fall" like other being.Splitting themselves into lower self(physical) and higher(ethereal).Or they can manifest as shadow,energy,voice for some time.
Are they shape shifters?
They are energy thus they can change form tho they are not immune to physical laws.
why or why not do demons attack humans?
They are higher spiritual being thus they don't attack or posses people.However they are made(one part) of dark energy and many other being(made of dark energy) posses or attack thus they think demon possessed or attacked them.Demons if dragged by some beginner and painfully bind into rune,circle will attack.But anything will.
Demons are ancient,wise teachers and warriors.High spiritual being.Tho made of dark energy some are truly beautiful.
Yup, only childish humans like the members of our society squabble over oil and petrol prices.. we stubborn humans invade other countries for it too.. Only children fight, yet, kids will be kids. The majority of our population are kids, mentally that is.
There are barriers between the physical world and the spiritual
and astral world. Their are gate keepers and such plus not all demons are the same but many have come thru various portals. Demons
are non corporal meaning they don't have fleshly bodies. This is why sometimes they possess people so they have a host to function
in our world. It takes a lot of energy for demons to manifest. Generally you have control over your body so it is up to you who you let in. There are exceptions like when you are in any weakened
mental condition. Plus people have guardians that they can call on to protect them from demonic possession which is rare these days.
yes demons can change shapes as many spirits can.