A way back when the earth was cooling and Telus was able to finally send a WiFi signal down copper from their exchange to our house and we were able to stop using "dial up" we were assigned three alpha-numeric e-mail addresses, each of which allowed the setup of up to three aliases giving us a total nine (ten if you count the primary ones). My wife and I used two each and one was assigned to #2 son as he was still at home. He has since moved on, married, started a family and living in an adjacent community. As he as moved about he has retained that e-mail address (he is still on Telus WiFi and Cell). How would one go about associating his Telus e-mail with his WiFi account?
Interesting. Your description varies a bit from my past experience, but let's start with naming things properly.
Telus provided you with an Internet account. It had up to 10 email addresses, and Telus apparently set you up with 3 email accounts which were further modified by adding aliases.
Wi-Fi is something you do with the Internet service provided to your house. Currently Telus router include a Wi-Fi function. It is not something delivered from the exchange.
I expect this is a rare request. What I think you will need to do is contact Telus and ask that Son#2's email address be transferred to his home Internet account. You should have your account number, his account number, and his alpha-numeric email address handy when you contact Telus. If it is rare, as I expect, it may take some time to go through the hoops to have this change effected, if it is possible at all.
In the meantime, he can continue to access the account as always, assuming you retain the 'parent' account with Telus.