Agree'd ~ if they aren't eating enough during the day, you must force it. Play a game, toss some kibbles...
I am not found of Euk. I think there are better qualities brands (Wellness, Merrick, Halo) just to name a few. Maybe they aren't fond of Euk either.
Next I would do Bile Acids (soon), as Liver Shunt and MVD are very common in the Yorkie breed.
Please keep us posted
