Put yourself in Washington's shoes. Someone's offering you Alcantara who struggled at the plate, Jen ho Tseng, who albeit great at A- ball is still at A- ball, and Travis Wood, who's taken a shit and is useless.
That trade gets laughed at. You'd laugh at it. There is no return for you if you're Washington. You'd get fired for taking the deal.
The deal is changed if Tseng was rocking at AA or AAA, but one decent year and 100 innings at A- ball isn't good enough.
I'd want McKinney and Edwards. I don't HAVE to deal him if I'm washington. Its not imperative because after 2015 season, they'll have a lot of money off the books, so resigning him is a decent possibility pending feelings on Dennard Span.
Also consider there are teams that could offer far better than your proposed deal for him. If you're washington, you consider that.