I tagged a few members that may be able to provide some insight on the weight issue. You may want to give the brand names of what you are feeding and the supplement so they can tell you the correct info.
as for potty, schedule is everything, I had the same issue with my Frenchie, took us two years to get him fully on board. He still does not indicate of tell us when he needs to go, we just have him on a vert tight time schedule when we are home.
How old is Steve and how long has he been with you?