Can gravity be focused by large massive objects?
Yes. The equivalence principle implies that everything is affected in the same way by gravity, including gravity.
This is true of gravitational waves. It should also be true of the static gravitational field, though I don't remember ever reading about it (or thinking about it) before. Probably, the gravitational attraction of two inline objects is slightly larger than a naive Newtonian calculation would suggest—although it's difficult to say what distances you should plug into the Newtonian formula when making that calculation.