I wouldn't run with anything more than the Basic Books, no matter what you players want. In fact, and I know this isn't going to make me popular here, if it was me I wouldn't run Rolemaster just yet, I'd start with HARP. But hey, if all you've got are the book for RMC... But before everyone starts shouting at me, let me at least explain:
First, being a GM is hard, it takes practice. I've done it for 6 years then stopped and now I'm getting back to it after 10 years. It's not only about the rules, it's managing the story, the pacing, make rulings like deciding which skill is the one to be used for that particular action, how hard/easy it is, determining what happens after the dice rolls, what are the consequences of the players actions, etc etc. All the basic skills that a GM needs to master first. And you're not making it easy on yourself by starting off with so many books to keep track on. When you learn how to drive, do you start by going to the most busy highway with a lot of cars running at 100km? No. You start small, first drive around the block, then eventually learning one by one all the little skills that would make you an acceptable driver.
You're the most important person at the table, if you're not enjoying yourself, you won't want to do it again, and without a GM, there's no game. So tell your experienced players to back off, cut you some slack and give you the chance to get good, because you won't be good at your first session, that's pretty much a fact. Especially if one of them is your dad, then tell him to be supportive, not a d--k. If you say only core book professions, then core books professions it is. They'll have to make do with whatever you say it's okay in your game. And if they don't like it, play just with your buddies. I repeat, if you're not comfortable running the game, your players won't enjoy it. In fact, make sure you are the only one making the calls and using the rules, tell the rest of them to put the books away. If you screw up, move along, don't stop for arguments about the rules. Be firm, don't be a despot, listen to them, but if you don't agree your judgement stands. You can discuss all you want after the session it's done, but never in the middle.
Once you get better at it you can start gathering feedback and such, but never run a game with rules you aren't comfortable with. The rules are a toolbox to be consistent and fair, not a straitjacket, and certainly not up to the players to decide how they work, it's up to you. They need to understand that in order for everyone to have fun, the GM has to be comfortable with the game. If you can't invision a world with Monks and they screw up your vision of your fantasy world, then you're going to do a poor job at communicating that vision to your players, and as a result you're all not going to have a good time. Of course, you should try to tailor your game as much as you can to your players wishes, that's all good and all, but as long as it doesn't involve you being uncomfortable when running the game.
I'll repeat: if you're not enjoying the game, then they won't. So in order for you to run a good game for them, you need to put yourself first. Note that I said first, not the only one. Because it's pretty obvious that if your players don't enjoy themselves, they won't come back. But that's all the feedback you need for now, at the end of the session, ask them if they want to do it again some time, if they come back then you've done a good job, and, for now, that's all the feedback you need.
Also, try not not start a campaign. Like I said, start small. Run a few independent adventures. Make everyone clear that after those are over, you're going to start over with new characters, this time for real. This way you got insurance that no matter how much you screw up(and you will), you know that in X sessions it will all be over and you can hit the reset button.
I'd also strongly advice not to run a game your dad and your brother know better than you do, because chances are, if they are temperamental, they will screw you. If your budget allows it get HARP, at least for the first sessions. Not only it's more newbie friendly, but also you will move your experienced players out of their comfort zone and they won't be able to argue with you nearly as much. And, if you are not great at it(and you won't, it's your first time), they'll blame the game instead of you. Once you're comfortable as a being 'the authority' on the table, you can move back to RMC and start you campaign or whatever you had in mind in the first place.
I know some people might scream loudly about my advices, but before doing so try to remember the first time you GMed. It wasn't easy, was it? Your goal here is to learn how to drive, step by step, little by little. Your father can't expect you to run games like he does if you never done it before, just like he can't expect you to drive for the first time like he does when he's been doing it for years. And learning how to GM is like learning how to drive for the first time in a manual car(like I did), not an automatic one: most of your efforts will be spend on not having the engine stop because you can't shift gears properly.