I would take it as "we also declare unto you that which we have seen and
heard," using KAI to connect the ideas of having seen and heard with that
of declaring. The context establishes John as an eyewitness of the
things he is declaring: "hO AKHKOAMEN, hO hEWRAKAMEN . . . hO EQEASAMEQA
. . . EYHLAFHSAN . . . hEWRAKAMEN KAI MARTUROUMEN . . . ." So, John
seems to be indicating that he intends to declare the things that he has
experienced in these various ways--to go beyond simply having experienced
them and add to the experiencing a sharing of the experience with his
readers. I don't see any grammatical indications that would get us any
closer to an answer than this, but I'll defer to the experts on that.
Trevor Peterson
M.Div. Candidate
Capital Bible Seminary
Lanham, MD