Hey Frankz, I'm nearly a noob myself. So let me welcome you to the forum. What you're talking about could be done easy enough if you
are out in the countryside where you don't have State Troopers breathing down our neck.
When we were kids we'd pull the front tires out of the forks of a few bicycles and loosen the nuts on the rear axles to make up bicycles for 2,3,4 and more.
Problem with Ohio, where I live, is that they clearly state "one rider" only. Some states may permit doing it but I don't know anything about it. I'm sure a traffic Judge would figure that anything boys do with bicycles is cool....but when they motorize and take to the road that that's a different matter.
So check out your state Motor Vehicles Web Site in the section of Motorcycles/Mopeds/motorized bicycles. (and if you put a motor kit on a bicycle, don't allow any Motor Vehicles Dept Clerks to refer to it as a Moped. It's a bicycle with a helper motor. Be sure to have your purchase reciepts for the bicycle and the motor kit. Trust me on this) They will likely want to sell you a license for the motor bike you build....which means a title etc. If you built it they will want proof of how and where you got the parts. (proving they weren't stolen)
So all the best with your project.