Help with Parts required

[Prophet]

Evening everyone!

I'm not overly tech savy with the new toys that have been coming out over the last few years... so please be patient with me as i learn this is all new to me...

My kids have asked me to build them a two player Arcade machine using the Ras Pi 3, however they may want a single machine each... ( they are both 12 so they probably know more then me!)

I have read as much as i can understand from the forum and through the help section as well as looking at other sites for information and watching a ton of youtube videos on the subject, many have been a little confusing as they all seam to be using a few different pcb's and software, making things a little over complicated with my project as now i'm unsure what i need to be purchasing to do this project..
I do want to stick with the Ras 3 and retropi as i've already programmed the sd card with the img and tested it with keyboard on the TV so i'm happy up to that point.

I've read here that you need the 'controlblock' to attach arcade controls( joystick and buttons) to the ras pi, will this support 2 players? and is is actually needed if i decide i want to build two separate single player units ? ( this gives me options as my kids like to play and fight as the same time) can the arcade controls be 'fitted' to the pins on the ras 3 like some youtube vids have suggested or are those misleading due to possibly using other hardware and software?

If i do need the control block is there a UK supplier? ( no problem buying USA just delivery's can take a while and kids are not patient)

So i was hoping some of you good gents would write me out an EXACT list of parts i do need to make either a single player or a two player arcade machine.
Money isn't an object but keep in mind spending silly money isn't going to wash.

I do not need the case, i'm well skilled with materials relating to building things, i'm a bench work and joiner by trade so the build is not the issue its the gadgets inside.

I appreciate your time and do understand if this has been asked before how annoying it is.

I will follow with more questions but will try to limit what i ask until i have exhausted all materials i can find to reduce the frustration of some of you.

Best regards.