This must be a really deep league.
But I would not do it. In a deep league, Castillo is not a bad 2B. You would be giving him up and getting no one who can really be called a good starter in return (I am not a huge Castillo fan, but he is little bit nicer to have then Cuddyer or Koskie). It would be the classic mistake of trading a guy who is a grade B fantasy player for 3 guys that Cs or Ds.
As for Gonzalez, he is not worth much. He is a Mark Grace/Wally Joyner guy, i.e. mediocre power. There is no spot for him Texas. Who knows when he may get traded an when an opportunity will emerge? Bascially, he is a guy with a very modest fantasy ceiling who will need to move to another club to even get to prove that he is a big league player. Not worth much in my opinion.