It would be a lot easier to create the fake ones if they didn't keep changing the design. I expect this new design is a lot more difficult to counterfeit.
Yes. You need much more specialized equipment to produce bimetallic coins that stay in one piece (even the royal mint had trouble with early production £2 coins). 12-sided is also harder than round. Also assuming the density of the inside and outside metals are different, then it'll be very easy for coin-accepting machines to reject fakes made of any single metal.
OT, but you never see many £2 coins these days.
I suspect people tend to hang on to them, because they are rather pretty and there's a new design out almost every year. I recently got a bunch of brand new ones out of a Sainsbury self-service till when I gave it a £20 note as payment.