If the children are replacements then it would be simpler for Prof and Mrs H to disclaim their appointment to trigger the replacements stepping in. Otherwise you will need medical evidence to confirm they have lost capacity to trigger the replacements. Either way the forms have to go back to the OPG to be updated to show that Prof and Mrs H can no longer act as attorneys so the replacements have authority to act. They will just stamp the forms accordingly and return them.
Maria Goodacre
Bells Solicitors Ltd