Having just finished the last of my Brewferm Abdij, I feel like making some more - quick

So I went and got 2 kits - only 9L each is a bit small for 9 weeks work.
Here comes the stupid question....
To make a double sized batch, would you just double up all the ingredients?
...seems obvious, but would you need 2 packs of yeast for instance??
Anyone done this already?
thanks, Jat