The current billing system does not allow for sharing. It's 1 line, 1 plan. It would take redoing the system to allow airtime sharing. Whether that's something Koodo is willing to look at, I can't say.
As a former employee of Virgin Mobile (I haven't really checked since but they were at least doing it in 2010) I can say that sharing minutes/data often works out to having one or more lines booted out of the shared plan for devouring all the minutes/data and leaving the rest in the cold for the rest of the month.