I walk Marty and Madeline together all the time. They LOVE their walks, but both were very stubborn about pulling on the leash and took a lot of work to get them to the point of ME walking THEM instead of THEM walking ME. lol! I'm so glad my husband and I spent the time to teach them to do it right cause it makes the walks a million times easier and more enjoyable for all of us.
I don't use a splitter, but it sounds like a good idea that may help. Good luck!