Changing landline number might help but may possibly make the situation worse. Any 'new' number will be recycled from a pool of numbers owned by VM.
There have been plenty of past examples on here of people making a number change, only to find they are still plagued by nuisance calls or have inherited a number with past business connections. It would be a lottery as to which new number you receive.
If your parents' number is still being abused for fake caller ID, then a number change might help but might also make things worse or no better. Something you should be aware of before making such a change not withstanding the inconvenience of notifying contacts of the number change.