Hi and welcome to YT
! He looks like a real little cutie pie! Those ears kill me, how adorable are they??!!
As far as leather ear, I don't know enough about it, but I'm not sure if you'll ever get hair there again...hopefully someone else will know more about this. He does look yorkie to me, despite his bigger ears.
For adding calories, I'd try things that are calorie-dense, such as bits of cheese and little blobs of peanut butter. You could also add bits of coconut oil to his meals.