yes
the gcf can be found by factoring the 2 numbers and finding the factors common to both
any even number can be represented as 2n where n is an integer
so 2 even numbers are 2n and 2m
their factored form will be 2*n and 2*m, currently, their greatest common factor is 2*c where c is the gcf of n and m
and the gcf has to be an integer so c is an integer and therfor the gcf of 2n and 2m is even because it is 2c
yes, it is always even