You guessed it... I'm contemplating on beginning a rather *small* campaign with my two brothers and possibly maybe get their girlfriends to play also. Perhaps not starting right away since we have tight schedule with my older brother having a job and my younger brother and me finishing University. 

First , let me explain where my I come from. My experience in D&D has been miniscule, I've been a player in a single 3.5 game of only two sessions (... Yep...), but I've been watching some shows on the internet like Critical Role, High Rollers and Heroes & Halfwits, so I know the basics and went out to read wikis and watching YouTube videos on D&D and DM'ing.

Very recently I bought the PHB and the Starter Set which has the Lost Mines of Phandelver module, thinking it might as well be a good starting point but here is the thing... Both of my brothers (and Gfs I'm guessing) know nothing about D&D, only that I casually talk to them about my only two sessions I had or when they see me watching an episode from Critical Role.

In any case, I'm a bit lost on how to go about this so I am here any of you could give any advice which is very much welcomed and appreciated, I'll try to answer your question and we can talk more about it.

Thank you in advance.

LMoP isn't a bad starting point.  The material you'll cover in the first two or three sessions is intended to ease new DMs into the game as well as the players.

If you use the pregenerated characters that come with the starter set they have backgrounds that tie into the material.  It's fine if they'd rather create new characters (and you always have the option of adjusting the material to suit whatever backgrounds they want in that case).

There's a lot of useful reference info and advice out there, but the #1 thing I recommend first is don't stress too much about knowing all the rules inside out when you're new.  5e explicitly encourages you to make whatever ruling you consider reasonable on the fly, and your main goal is to make sure everyone has fun (including you).  If you want a good example of a bunch of people who have never played D&D before having fun with Lost Mines, check out the first few episodes of the McElroy brothers and their dad in The Adventure Zone podcast.

You might try playing out the initial goblin ambush by yourself ahead of time with a few of the pregen characters to get a feel for what the moving parts are when you're managing combat. 

Just remember that when you're playing live, it's possible (likely, even) that the players will make some decisions you don't expect.  That's cool.  Try to roll with it, and have the NPCs/monsters react in ways you think make sense, even if it ends up taking the adventure in directions you might not have anticipated.  Some of the most entertaining sessions can happen when things go in unplanned directions.

Good luck, and have fun!

If you have seen just about any movie with a fantasy setting, you can touch base with D&D.

Talk to the players about what kind of heroes they want to play.

Help them create characters. There are about an equal number of people who will say pregens are best for new players and those that say rolling their own is bets for new players. I like roll your own because it has more ownership for the player.

Read through the basic rule set thoroughly. It meshes very well with LMOP and LMOP has many tips within it to help new GMs.