First yes, you want to create a player for yourself so that you can participate as a team in the league.

There are two ways to run the league - either you can email files back and forth or move them on a flash drive or whatever is most convenient for you being in the same house or you can setup a FTP server and move the files over the internet. With only two of you in the same house the former may be the easier option.

The files you will want to share with your son are the league files. In the saves folder you will find a .pbb file for your league AND a folder. You will want to give him those files to place in his app/disk/saves folder for the game on his computer.
​
Then to play you will both login as your players - on your computer you can make your changes and decisions and simply save the game. Your son will login on his computer, make his decisions and then there will be export buttons he will need to click - the majority of the time he will want to export from the Your Office link on the left and on that screen there will be a Export MP File button. He should save his game prior to exporting the file as well. Once the file is exported he will want to look in the app/disk/Multiplayer/yourleaguename folder to find the file(s) he exported. Copy those files and place them on your computer in app/disk/Multiplayer/yourleaguename folder (and you may have to create the folder in the Multiplayer folder for your league - so if your league is called NBA then you would want to create a NBA folder in app/disk/Multiplayer). Then you login as the commissioner, go to the commissioner office and click the button to import the files. Then you advance, save, exit and follow the first instructions to send back the updated league files to your son.
​
As commissioner there will be some things you have to do - if he wants to sign free agents during the season he will have to instruct you to sign the player which you will do logged in as the commissioner. Making trades would be the same thing. Anything else you would be required to do the game will notify your son to ask you as the commissioner to do it. This is done because the files have to match when importing so if he were to add a player to his team then the file would not match what you have as the commissioner and cause a problem etc...
​
Now, the majority of the file moving can be done via the internet but you would have to get hosting space and understand how FTP works so being in the same house it may just be easier to hand off a flash drive.
​
What I would suggest is to setup a second league and just use it as a quick test to test out things and make sure you have the hang of it and then start your real league.
​
If you have any questions the community is great to help answer these things or you can ask questions here and we will respond as soon as possible.