S.D.
This might sound crazy but I taught my b/g twins to drink from actual cups starting at about 5 1/2 months. It was frustrating, but with two, I didn't want to be unable to feed them both at the same time...so, long story short - they transitioned into any type of drinking! Straws, cups, sippy cups, you name it. They are two and will sit at the table and drink from cups - even better, if they find an unguarded cup it doesn't get spilled...they just drink from it! :) I would actually recommend trying to teach them to just drink from a cup - it will be messy, but won't take long! Then, start with the sippy cup. It is backwards, but nobody is the same!
let me know how it goes.
S.