What compression setting are your textures set to right now (it should say something like RGBA, DXT1, DXT5, BC5, etc… in texture editor)? Do they have alpha channels?
ETC1 is a miserable compression format that does not support alpha channels, so any RGBA textures, even if they ‘DXT5’ on PC, will get stored as full 32 bit textures when cooking for Android (ETC1). One common approach for Android is to split your sprites up into two separate ETC1 textures, one for RGB, and one for A. These two textures will use 4 bits per pixel each for a total of 1 byte/pixel versus 4 bytes/pixel. You can then use a material to route second texture read into alpha result of sprite.
Cheers,