The word "Yes" shows that Jesus is adding to what he was saying before.
# it is written
This is a passive phrase. You may translate it in an active form with a personal subject. AT: "Moses wrote" (See: [[rc://en/ta/man/translate/figs-activepassive]])
The logic implied here is that one person can verify the words of another. AT: "if two men say the same thing, then people know it is true" (See: [[rc://en/ta/man/translate/figs-explicit]])
The Father also bears witness about Jesus. You could make it explicit that this means Jesus' testimony is true. AT: "my Father who sent me also brings evidence about me. So you should believe that what we tell you is true" (See: [[rc://en/ta/man/translate/figs-explicit]])
This is an important title for God. If your language must state whose Father this is, you could say "my Father" since Jesus switches to that in the following verses. (See: [[rc://en/ta/man/translate/guidelines-sonofgodprinciples]])