Cancelling phone and broadband

Not sure where to start on this one.
My parents have just moved home. Had a BT phone line with O2 broadband in the old place. Have SKY phone and broadband in the new place.
So basically, do they have to cancel the O2 broadband first, wait for the 30 day period, and then phone up BT to cancel? Or can they cancel both on the same day? (obviously they would still have to pay O2 for the 30 day period).
Bit of a dull question I know, and don't really know which section to put it in.
Cheers.

Both services may have a 30 day notice period, you can usually specify the date when you want both services to physically stop working in advance.

If you cancel both 30 days before leaving property, there is a chance they may get cancelled a few days earlier, so be prepared