# the life was made known

"God made the eternal life known to us" or "God made us able to know him, who is eternal life" 

# we have seen and testify

"we have seen it and testify about it" or "we have seen him and testify about him"

# the eternal life, which was with the Father, and which has been made known to us

"the one who enables us to live forever, who was with God the Father, and who has been made known to us". This refers to God the Father. It is best to translate "Father" with the same word that your language uses to refer to a human father.   

# and which has been made known to us

 "and which the Father has made known to us"