Hi Celine, You could separate your account out of other person by doing a transfer of ownership ($10). Your grandparents need to authorize it also. It would be convenient if both of you can visit a Koodo Kiosk to do it. You would have to create an postpaid (monthly) account.
You could also do it over the phone, your grandparents need to cal them first, then you can call in and make the transfer.