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.

Your main barrier is the amount of lore knowledge that the player base will have (which sounds like near nil) therefore unless you want to spend ages explaining everything to them you may want to keep it very simple and avoid going into too many details. Black Crusade can be fun for that as you don't have to worry too much about the lore or belief of the Imperium, the various religious or organisational concepts and all you have to worry about is being bad...which should be easy to do.

Alternative, be a guardsman and do Only War, where your job is to drive tanks, fight and die. It's a simple lifestyle and concept.

Rogue Trader i'd say. it is closet you can get to a traditional RPG fantasy setting as a group of adventures going out to explore the world and fight of evil.

in this case the world is the galaxy, and you arnt a small group, you & your group are the head of a dynasty with hundreds of servants. but still it gives you alot freedom to do what you wish.
compared to the other 40k RPGs where it kinda mission based. you get a mission in a way from a NPC that has a higher status than you and you have to carry it out.

Stick with the basics. Try to avoid complicated lore points. They are not going to understand all the many details of the warp and the different gods in it and how they all interact with each other. Keep it simple at first. Xenos are bad, we kill them because they will kill us if we dont. If they become interested in the lore more, then you can feel free to add more.