I agree with Krikkit. Work one dog at a time. And then work them together. Get mastery of walking properly, at your pace, with a loose lead with one dog at a time. Then you can teach them more easily how to be on the right or left side, or split.
I work my two a lot on our walks. Our only "issue" was that Susie INSISTS on being inside next to me. Maggie had to learn that she has to walk with Susie in the middle. Didn't take long to get it down but at first it was a bit disconcerting for Maggie.
We have great walks now. They move behind me to the left or right side on command and split (one on either side) on command as well. Luckily, we lived in an apartment so we took LOTS of walks and got in loads of practice, so it wasn't too long before we were enjoying long pleasant walks, just the 3 of us.
Good luck.