Thanks for your reply canuck78.
This idea is about to let parents to have flexibility to stay for either short term (week/weeks on visitor VISA) or long term (months/years on super VISA). I think that super VISA also allows for short term stay, but it always requires insurance. Just thinking, if just staying a week, won't worth to pay an insurance, so might be good to have visitor VISA as well.
So appreciate if there is an answer for if visitor VISA and super VISA can be applied at the same time, or can they someone still to apply visitor if they already have super VISA and enter by visitor VISA.