venom by as slot

Sorry, to ask this but I am not understanding two thing. 1) I notice people in their army lists are taking venoms but no one in them or dedicated to a unit.  How can you do this?   2) Also another question is that I am seeing army lists with elder Allies and they saying they are in a transport with unit  a archon or some other HQ with a WWP how can this work.  I understand they are battle brothers so they can embark in each others transports.  I thought that the allied unit would have start on the board then embark in the transport first round.  Which would then make the WWP useless if this is how I believe it works.  If I can receive reference where to go if I am wrong it would be appreciated.  Just like to have the back up for this.

1. Page 86 + 87 Dark Eldar Codex
2. Functionally page 82 of the BRB is the core answer here - the dedicated transports entry contains all of the limitations (beside unit size and unit type) to starting embarked on a transport of your army formation or that of a battle brother.

1/ Two possible ways. First, taken as a Transport, but deployed separately. Second, Raiders and Venoms can now also be taken as separate Fast Attack choices. In the Codex, pages 86 and 87.

2/ As Thor says, on page 82. It is now possible to start embarked, within certain limitations.

Thank you for answering this for me.