Okay, so I am new to RPG's both as a player and as a GM. I own most of the rule books for Rogue Trader, Only War, Black Crusade, Dark Heresey(1st e) and Deathwatch. My family has finally agreed to entertain the idea of playing one of these games with me. I like to think that I have a decent amount of knowledge with the 4ok universe, but my family has none. I will have both male and females players. up to three players total. I was wondering if there is any suggestions as to which universe to introduce them into the 40k universe while also keeping it easy for all of us having no RPG experience. (I mostly collected the books for a personal collection point in hopes eventually I'd find someone to play with). Any suggestions or feedback is greatly appreciated.

I started with Only War, and I would recommend you do the same with people who have little or no experience with the 40k universe. OW is the easiest part of the setting to grasp, as it is basically WWII soldiers with laser guns. Nobody in my group knew anything about 40k when we began, but OW provided a good way to get their feet wet.

In addition, it is easiest to role play. Everyone knows how soldiers are supposed to act, and what they are expected to do. Defining the nebulous responsibilities and expectations of a cell of Acolytes or the retinue of a Rogue Trader is more difficult.

Yeah, I'd go with Only War. If you can, for a quick introduction for the Imperial Guard as a faction, let them all read the Uplifting Primer.

yeah only war. Rogue trader has too much background, deathwatch will give them realistic expectations about future games (e.g. in deathwatch you might kill 100 orks in 1 session but only war struggle to kill 10),

black crusade might be a bit wierd with your family, like if you'd find it awkward if your mother seemed to be having fun role playing a sadistic bloodthirsty killer then dont play black crusade

tbh dark heresy would be ok

You should watch a few RPGs being played online.

ItmeJP on youtube, has the best RPG shows on youtube,

https://www.youtube.com/channel/UCQj4ZJd2QxRHwVYQbMvcKdQ

You should also watch this show, it's done by the person who co wrote dungon world, as well as the lead level designer on eternal crusade.