For the person who asked and then deleted while I was typing:
I'm not a native English speaker nor am I any good at explaining but I'll try.
You can download all the files, base + dlc 1 & 2 or you can only download dlc 1 and 2 because the dlc files also include the base game. The latter is easier.
So it's DLC 1 file = base game + dlc for step 1.
DLC 2 file = base game + dlc for step 2.
If you instal both dlc files and you already have the base game installed, the file will only install the dlc. It will say also update instead. It won't increase the size of the game (So it won't go from 591 mb to 1.1 gb or something)
If you're strapped for space, it'd be wise to download and install the dlc 1 file. After it's installed you delete the downloaded dlc file and download and install the dlc 2 file and then delete that one.