Art is right, you thread a double needle from the inside to outside, and the needles have to be in the proper position. If you are used to a single needle machine you know how to install the needle with the thread groove, with a double machine the right needle is the same as on a single needle machine, but the left needle is put in opposite (thread groove) of the right needle. According to your third picture you have the left needle threaded wrong, the thread should enter the inside of the needle and exiting through the outside.