Van Wolfswinkle & Fer have both been less than stellar, Bony has done okay, although 2 of his 8 were in the last match, but he has a respectable total.
To just defend our own players....
Van Wolfswinkel has been out injured since October and today was his first start since then. He was also forced to play several games carrying an injury. His problem is that he's simply too good for our midfield. His movement is absolutely stunning, and he's good in the air and has an excellent touch, but we don't have the midfielders to play the through balls he'll thrive on, nor to cross into the right areas consistently. At a better club I think he'd score for fun. We also try to aim long balls at him too much, which whilst he's not too bad at, isn't his natural game. I think Bony would have fit in better with us, and RvW at Swansea to be honest.
Fer was our best player early in the season, but his form has evaporated over Christmas. He's good going box-to-box but our injury situation has forced him to play deeper which doesn't suit him. Also works best in a 4-5-1 but we seem intent on playing 4-4-2 at the moment.
The Dutch league appears to have some bargains, but they aren't all going to work out. Same as from anywhere I guess.