Hi

My Parents both have I phones and are on the same i tunes account. They want to change this and have there own i tunes accounts because when there's updates and stuff things get messy and things go wrong like contacts get mixed up and lost.. Will all the Photos and Videos stay on the i phone if the account is changed? Also how is the best way to do this.

Thanks

Just reset phone, setup as new and create a new AppleID.
Yes the photos will and videos will be deleted, but you can remove the photos and videos first by just connecting to a computer, select phone from connected devices and opening the DCIM file which the photos are stored in and transfer them across.
Or if they use Facebook you could always upload them to that.

My wife and I have seperate phones on the same iTunes account, but we have seperate iCloud accounts so whilst we share the saem apps and music/films etc we have our seperate photo roll, calander and reminders.

Yeah that's the best way to do it, no point buying apps twice.

You don't need to buy apps twice.
All you need to do is to go into App Store settings on phone and change the Apple ID & password to the one who purchaed the apps and just click on the cloud icon and download it. Then change your Apple ID & password back again.
Obviously that app won't be linked to your account if you delete it, but you can use apps fine.
It doesn't work with Music & Video purchases though, but you can still get round that by putting the iTunes library on a computer into the shared folder.(as long as all idevices are synced to the same computer of coarse)

Far easier just to share the same iTunes account and have a separate iCloud account IMO.