“You know” is a grammatically possible translation of the first word in Greek, but “Know!” or I want you to know is more likely. Brother has the special Christian sense of “fellow Christian,” implied by 13.1. Let out of prison: of prison is not expressed in the Greek text and is not absolutely necessary in translation (literally, simply “released,” Revised Standard Version), but it seems the most likely meaning. Good News Translation, Die Bibel im heutigen Deutsch, Barclay make out of prison explicit, but most translations do not.
The most likely explanation of the second part of the verse is that as soon as Timothy joins the writer, the writer will take Timothy with him to see the readers of this letter (compare verse 19). “As soon as” is a well-attested meaning of the Greek words translated soon enough, but has not been chosen by translators. Parola Del Signore: La Bibbia in Lingua Corrente has simply “quickly.”
For I will have him with me, Bible en français courant has “I will take him with me”; Translator’s New Testament and Die Bibel im heutigen Deutsch have “I will bring him with me.” Bible en français courant takes as the point of reference the place where the writer is; Translator’s New Testament takes it as the place where the readers are. The translator must decide which is more natural in his own language. In English, as well as in this context, both are possible, and also Good News Translation‘s neutral I will have him with me. However, the use of “bring” rather than “take” suggests a warmer identification with the readers’ point of view.
Quoted with permission from Ellingworth, Paul and Nida, Eugene A. A Handbook on The Letter of the Hebrews. (UBS Handbook Series). New York: UBS, 1983. For this and other handbooks for translators see here .